Herrickmky

Hi, all, would like to learn from you any idea regarding my M104.980 engine's high idle issue.

Some background info of the car

• 92 manufactured
• M104.980 engine
• 180,000 KM on the clock
• European spec (Hong Kong registered, import by dealer)

Before the current high idle issue, the following components are replaced with new parts in a time span of 2 years

• EHA valve - to fix fuel leak
• Intake air temp sensor, idle control micro switch, ICV, OVP and Bosch Airflow Potentiometer - in the attempt to fix high idle issue. At the end, the high idle was fixed by the new airflow potentiometer
• Ignition coil, HT lead, spark plugs, distributor cap and rotor - in the attempt to fix engine stall after engine hot. At the end, the issue was fixed by renewing the heat disperse paste under the EZL
• Camshaft adjuster - forget the reason
• Fuel pump, fuel filter, fuel pressure regulator, camshaft position sensor as preventive maintenance
• Air / Fuel ratio adjustment screw has been fiddled around to tame the emission for MOT purpose
• New alternator - old one was dead and do not charge the battery

In that 2 years, the car was running well with this and that issues solved

The current high idle issue
All of sudden, the high idle issue occurred again. The symptom is as follows:

• Engine start normally, idle at 900, 1000 rpm and stays there. does not drop to 750 rpm as normal. In 1-3 minutes, idle rises to 1600 rpm itself and stayed there without touching the throttle pedal at all.
• Depressing the throttle pedal, 2 scenarios are presented.
  1. RPM rises but don't return to 1600 rpm but stays at higher, 2000, 2600 rpm depending on how high it had risen
  2. RPM does not rise, airflow sensor plate does not go down

I've tried disconnecting the ECU, all the same things occur except that the RPMs at the start usually is lower, sometimes at 600 rpm or 700rpm, then rises to 1600 rpm

Diagnoses and action done (With no success)

1. Adjust the air / fuel ratio with the adjustment screw
2. Replace the airflow potentiometer with a brand new one from after market brand
3. Test the continuity between the end of ECU cable leading to the ECU and the relevant sensors, between MAS and ECU - all are fine
4. Test the following sensors
5. TPS - both full throttle and idle position signal are fine
6. Coolant temp sensor - temp vs ohm value are fine
7. OBD 1 reads Crank Position Sensor error, cleared and come back after each restart - replaced with 2 new sensors, error still present. With a different ECU, error still present
8. Duty cycle measure and adjustment -
   1. VP3 indicates rich mixture -
      You Tube
   2. Adjust the VP3 by adjusting the air/fuel ratio screw -
      You Tube
   3. Next start, the duty cycle resumes to rich mixture -
      You Tube
   4. One day, the VP6 does not fluctuate anymore and duty cycle stuck at 10%
9. ICV test
   1. ICV voltage 5.67v at 1600 rpm
   2. Unplug ICV during 1600 rpm, idle drops to 1100 rpm. Plug it back, idle remains at 1100 rpm
10. Adjustment the airflow potentiometer position, and set the voltage at 0.7v, rpm drop but resume to incorrect voltage at next start. Very similar to the duty cycle situation
11. EHA test
    1. EHA value current - 20mA
    2. Unplug EHA, idle RPM NO Change
12. Test with another used MAS - no change
13. Fuel pressure measure
    1. Test fuel pressure - System pressure 6.1 bar, control pressure 5.8
    2. Turn screw in 0.25 turn, no change
14. Rebuild fuel distributor by an expert in Australia
15. Install new Bosch fuel injectors and injector rubber seals
16. Cold injection valve test
    1. Unplug cold injection valve plug - no change
    2. Block fuel supply to cold injection valve - no change

That's all I can remember what we have done.

What I'm going to do next

1. Test with another ECU to see if it makes any difference
2. Check the cable continuity between the EZL and ECU
3. Check the EHA current again

Any thought is appreciated

dolucasi

Thank you for posting your own. A caveat here, my knowledge of M104 with KE-JET emissions is very limited, just read some posts about your engine management issues.

You have a unique (limited to 1-2 years of manufacture) ECU/MAS and EZL. Generally for a well maintained car like yours with many components replaced with limited success the problem is the EZL.
I say this because I have read posts about EZL issues of your model. The Standard EZL on M103 engines hardly fail. They have been field tested with millions of cars on the road for decades. Not so with the M104 engine.

The fact that you are getting crankshaft sensor error code points in that direction. Also the fact that at some point replacing the thermal paste made a difference is another. On an M103 engine that is generally not an issue, I think because it is overdesigned and does not have overheating issues. My guess is the M104 version is not so.

You need to first somehow get rid of that error code. My guess is you replaced many parts that did not need changing but that does not matter as long as you used quality OE parts.
Since the engine rpm is controlled by the EZL from an ignition point of view this is quite likely that is the issue.

If you can swap your EZL with a good know unit (and not spend 100's of dollars) that would be a good start. Your EZL will be hard to find after 30+ years. With a car like yours you should store a known good EZL at all times as one of our skill level can not diagnose or fix them. I have 3 EZL's in stock myself, even though M103 EZL's are solid.

One last long hanging fruit is the folowing: The M103 engines have the low voltage ignition signal jumped at a receptacle bolted to the driver side fender (left side). This jumper is completely exposed for an unknown reason and I have seen one case where that jumper screw was loose. Not common but happened to this person. Check to see if you have an exposed jumper like the M103 engines. A problem here causes no starts but who knows. This receptacle is a black round plastic thingy of about 5cm in diameter.

But overall the OBD is already telling you there is an ignition issue.

One other thing completely unrelated is you never reported O2 sensor readings. If not done, you should do that. Especially if you do not know the age of the O2 sensor.
Your duty cycle readings are probably misleading you into adjusting your AFM lever adjustment screw. I would stop adjusting that, fix the other problems then go back and see if you can center is again.

-Cheers!

Herrickmky

of the
Hey, thanks! Regarding the EZL, I once thought it is the root cause but switched my attention to other components as the MAS does receive the engine speed signal from the EZL and relays it to the RPM gauge of the instrument cluster and the ignition is strong. Guess that I may need to reconsider it as the root cause. And yes, the M104.980 EZL is bloody expensive and not many are available with proof of working. Anyway did some tests today with another ECU and the results are as follows:

Installed an used ECU from Ebay

1. Check the stored error code - no code stored in the ECU
2. Ignition on engine off - Crank shaft position sensor error emerges immediately without even start the car --- another strong piece of evidence pointing to the EZL
3. Engine start with no hesitation
4. Idle at 1400 rpm
5. EHA current behaviour is shown in the following video :
   You Tube
   is the EHA behaving normally?
6. Pull the throttle cable and release, RPM rose then RPM stuck at 2200 rpm - same issue with the original ECU, so ECU can be ruled out as the cause
7. Unplug the EHA connection, no change to the 2200 rpm
8. ICV voltage at 2200 rpm 7.83v
9. Unplug the ICV, rpm dropped to 1000 rpm, plug it back , rpm remained at 1000 rpm. - same as before
10. Unplug the vaccum line to EZL, idle dropped to 950 rpm
11. Engine is running rich, carbon is found underneath of the exhaust, a lot of black smoke from exhaust

As you mentioned, something is causing the ECU to raise and keep the high idle.......ECU itself should not be the problem

As suggest, I also measured the O2 sensor value

At that moment the engine temp is around 50 Celsius, it took 2-3 seconds of cranking to start. Start at 1200 rpm, rose to 1400 rpm immediately (O2 sensor is disconnected from the ECU)
While I moved on measuring the voltage, the RPM dropped to 1200, 1000 and 900 and stayed there; engine was running rough and rich while black smoke was coming out of the exhaust
O2 voltage at the beginning was 600 mv and quickly went up to 720 mv, then moved between 690 and 710 mv. it looks to me that the O2 sensor is ok as engine is running really rich

Duty cycle
Reconnect the O2 sensor, restart the engine again at the time engine temp is around 60 Celsius, again took 2-3 second to start, idle started at 750 rose to 900 immediately
Duty cycle reading at VP3 port started at 6.87v, quickly climb to 7.x, 10.x then settled at 12.5v while voltage at VP6 is 14.49v
Pull the throttle cable, RPM hesitated to rise, pull harder, a big pop from the airflow plate, then RPM rose, release the cable, RPM dropped to 900. hmm, sometimes, it dropped back , sometimes it stayed high
Again a lot of black smoke and spark plugs were covered by a thick layer of carbon

Will see if I can find a proven EZL for testing

Cheers!

dolucasi

You seem to be well equipped with meters and such since you own a fluke meter. I'm hoping you also have a strobe light to check timing.
I would also take a peek at your timing. If there is an EZL issue it may show up there. It is possible that you are not running rich but the timing is all messed up.
It is a possibility. I say this because your EHA current looks perfectly normal. 20mA with ignition on, jumps high during cranking, Then assuming the engine was well below operating temp it is a high value and gradually comes down. Unfortunately your temp gauge was not showing so I could not tell if you ever get to operation temp because I did not see the lambda going into closed loop at the end.
Good to see your TPS behaving and the ECU responding to the gas pedal as it should while engine is cold.

The erratic behavior you are seeing is common when some critical component is malfunctioning and the closed loop systems (idle control, lambda control, etc) is just trying to find a steady state condition and can not. I have seen it in my car in which the idle can even start wild oscillations.

So I would say if you do not have a strobe light, buy one, they are dirt cheap.

Herrickmky

will get a strobe light from my mechanic and learn how to use it.

in your opinion, would the timing issue (if there is) inter-related with the high idle? Or they would be 2 separated issues

cheers!

dolucasi

Since the ECU/MAS get's the idle information from the EZL I assume it is possible, especially if that info is wrong or erratic.
Ignition issues generally cause a no-start/stall but who knows. Strobe light is the best and direct way to find out if at least the timing is right during high or low idle.
Your engine is still in running condition so it makes this test easy, a bit more complicated if it was not running.

I wonder how the ECU determines there is something wrong with your CPS signal. Maybe there is no signal to the ECU but the low voltage signal is still present to the coil(s). I assume your M104 has a coil pack so it is really 4/6 signals, entirely different from the M103.

My assumption is that the ignition fault causes the ECU/MAS to force a predetermined (higher voltage) signal to the IACV.
And since this is determined by the idle controller, it maybe an active signal meaning everytime you are going from running to idle it is re-evalluated and perhaps it is different result from time to time. I really do not know. But we will find out soon ....

Herrickmky

Got the strobe light and have done a check. However, not sure if the reading is useful. I could barely find a very narrow gap from that I can see the crank shaft pulley but no TDC mark can be read. Anyway, the number I can read at 1000rpm is either 5 or 6 underneath the right side edge (looking from the bonnet to the boot direction) of the front crank shaft position sensor. The engine temp is at 60 Celsius. I was unable to allow the engine to run up to 80 Celsius as too many black smoke is filling up the car park space. And I'm trying hard to find the suppose-to-be ignition time.

And indeed, in the first minutes, the strobe light didn't flash indicating no spark at spark plug 1. I checked with the other 5 HT cables, the light flashed as expected. I got back to the spark plug 1, it started to flash intermittently, only a minute later, it flashed constantly. Unfortunately, I can take a clear picture
Check the HT cable ohm, all cables are fine as they showed more or less the same readings. I'm going to disassemble the distributor cap and check the condition of those metal contacts inside

dolucasi

I suspect you are dealing with 2 issues now that you have to resolve separately.

(1) It seems to me there are some issues with the HT signal you are getting. So your car has a standard single coil + distributor ignition not the 94-95 M104 coil packs? Certainly check the distributor, you should never get intermittent strobes like you witnessed. Repeat the testing if you have to, sometimes these can be false positives. However the high tension issues should not throw codes, it must be the low tension signal that is busted from the EZL. Also double check your cluster gauge (low tension signal basically) against the low tension signal at the coil with an engine analyzer meter (just a handheld one would do). You can get the dwell angle too from the analyzer. Yes indeed, this is old school diagnostics and those tools that were used 40 years ago and long forgotten do come in handy.

(2) Your EHA current is normal before the operating temp range so the black smoke could be due to unburnt fuel in one or more cylinders, but it could be that since you fiddled with the AFM plunger adjustment, the adjustment is way off now. It is hard to adjust that back if we can not trust the lambda system. The only way is to use a tailpipe sniffer to minimize your emission readings as you are adjusting AFM plunger screw. Your oxygen sensor readings are bad, not sure if you can use that signal to adjust. Do you trust your O2 sensor? How old is it? Hopefully it is not the original, they do not last that long. They usually only go 120-140Km before the CEL is thrown at which point they need replaced. You did not mention replacing the O2 sensor in your initial post, thus the question.

Herrickmky

Today is fairly occupied, so no update on testing. Instead, I'd like to answer some questions raised.

The car has the CIS-E and MAS taking care of the fuel supply and EZL + a single coil and distributor ignition for ignition. It is not the HFM and LH Jetronic with coil packs
While it is running rich, I'd say all cylinders are running rich as all spark plugs are covered by the same amount of carbon (gauged by visual inspection)
The O2 sensor has been replaced after I got the car, indeed 4 years ago. Since then less than 10K kilometers are added to the clock

One situation I haven't mentioned is that when I were dealing the high idle, one day, the engine once refused to start with a lot of fuel covering the spark plugs or a big cloud of black smoke emerged if starts then stalled in less than a minute. To get it start, I used to turn the AFM adjustment screw counter clockwise one turn each time. By doing that, the engine's start getting improvement - it started at least, shorter crank time before start, Idle started from 350rpm, less black smoke and less carbon on the spark plugs. After 6 CCW turns, I got the engine back to "Normal" - Engine starts sharp, no visible black smoke, clean spark plug but the high idle issue mentioned also resume. then I go on doing the test stated in my first post. Without making any change to the A/F, while I was doing the test stated in above posts, the engine becomes to run rich again with black smoke coming back, very strange.

May I also have your help to elaborate a bit more regarding the high/low tension signal? It is something new to me.

Tmr I should be able to check the distributor cap

Cheers!

dolucasi

Sorry I had some mistakes about the engine analyzer and high tension measurements. I corrected my earlier post. Engine analyzers measure dwell and rpms from the low voltage side of the ignition coil. You can do this if you had an analyzer to make sure what your instrument cluster is telling you is correct, plus it will tell you what the dwell angle is. So if there is something wrong with the EZL, it may, just may show up there. You may get unstable dwell for example. I have done this testing once and also I can read my rpm as I am doing work under the hood with the analyzer.

I'm pretty sure there is something wrong with your ignition and most likely at the low tension side because your ECU is telling you there is something wrong. It would be good to know what sort of unexpected value throws that code. I do not know the answer. To be honest on the M103 engines, I have not heard of any cases with that code, so it must be rare or maybe uniquely rare for your model.

1) One question I do have. You talked about measuring the O2 sensor voltage with it unplugged. That is not how it is normally done. It should be plugged in. Because if you unplug it, you have messed with the close loop operation and you will get some strange readings in my opinion. So if not done so, please repeat that with the O2 sensor plugged in. you are supposed to use a thin copper wire and jam it into the barrel connector to get at the signal.

2) With the severe AFM plunger adjustment you have made, I am sure your adjustment is way out of whack. Remember these adjustments are like 1/6 a turn to align, maybe even less, not multiple turns.

Trevor Hadley

Did you check the small micro switch on the throttle lincage ? Along with fresh air sensor.

Herrickmky

Hi, Yes, both are new and checked signal presence for the switch and ohm for the air temp sensor

Cheers!

Herrickmky

When I did the O2 sensor test, I unplugged the signal cable, connect the male end to ground, connect the female end to meter's positive, then connect meter's negative to ground. Wondering if it is the right way to do the test. As signal is not going to the ECU, so i thought it is disconnected. Anyway, will do it again with it connected

Eventually . had time to disassemble the distributor cap. each contact point has some powder-like white substance on it and a burnt mark.


The substance on the 1st cylinder looked a bit bigger

Not sure if it is the cause of the intermittent not firing. I'd just clean all the contact points anyway. BTW, you can ignore the jelly-like substance at the edge, it is dielectric grease I used to seal the inside of the cap from moisture

After cleaning the contact points, the intermittent not firing on cylinder 1 seems fixed according to the strobe light check, However, some continuous "popping" sound and shaking can still be heard / felt, like misfiring. And black smoke can still be seen. will do a few more rounds of examination in the coming days and see if I manage to find a time to run the engine up to the operating temp

dolucasi

Yes, that is a disconnected measurement. You may have a different O2 sensor. Mine only has a barrel connector with a single wire. The ground is chassis ground. So you stick a non-stranded single copper wire into this connector as you are pressing together and clip on the positive end of your meter to this wire. The negative end of your meter is connected to a chassis ground in the vicinity. The door strike plate is generally good and convenient. Repeat this test and report please.

Also please take a close-up picture of your distributor rotor. Might be interesting to see what that looks like.

Overall, I believe all the arrows are pointing in the ignition direction but that does not rule out other additional issues. Certainly there is unburnt fuel coming out the tail pipe.

(1) Where is this popping sound coming from? The throttle body/AFM area or the tailpipe?

(2) How easy is it to start your engine when cold?

(3) Have you checked your HV pin in the middle of the distributor cap? Is it making good contact? That actually is the Achilles heel of these distributors. Check if the spring is in tact.

(4) What happened to your error code on timing? Is that still present? I'm not sure bad HV circuitry can cause a LV error code. It would have to be seen on the LV side. That might be possible but I'm not sure.

- Cheers!

Herrickmky

Hi,

Yes, I did. the micro switch is fine and indeed it is a new switch. Fresh air sensor, if you mean the air temp sensor, I'm going to test it, will revert here soon

Herrickmky

Since it has been the lunar new year, has been occupied. Eventually, had time to do the test again
I tried recording the idle rpm, temp, EHA current, duty cycle and O2 sensor reading throughout the test. However, the duty cycle recording didn't go well, as a result, I don't have the reading of the duty cycle. Anyway, the following is the summary
The entire test lasted 24 minutes, but until at 23 minutes, I have not touched the accelerator, just let the car idle. The data can be divided into 2 stages
1st stage Min 0 - 4 after engine start

• RPM: started at 1300 rpm, drop to 1100 rpm immediately and sat at 1100 steadily
• EHA current: Started at 16 mA, in a few seconds, drop to 4.2 mA, then gradually drop to 1.56 mA in 4 mins
• O2 sensor: at 3 mins, it was 371 mV
• Duty cycle: Start at 4.77v, went up to 7.6v, then I lost the data till 7-minutes after engine start. 7.6v, sounds good to me though
• The engine run rough, constantly had small shaking, in the 1st min, the shaking was worse then improved a bit
• At the 1st min, ignition timing is BTDC 10 degres, at 4th min, it became BTDC 15 degree

2nd stage Min 4-22 after engine start

• RPM: from 1100 rpm gradually dropped to 600 rpm within that 18 mins time span
• EHA current: between min 4-5, the current once drop to 0.8mA then rapidly went up to 9.95mA, then stayed there till the engine stall, I reckon this is turning point
• O2 sensor: at min 7, the value was 656 mV, then gradually rose to 730 at min 22
• Duty cycle: don't have the value between min 4-5, so can't see the relationship with the EHA current. From 7th min on-wards, it was 2.18v-2.24v, % is 8.9%-9.3%
• As the RPM dropped, the engine shook more. And black smoke from the exhaust became visible and getting worse
• While the idle dropped to 900, ignition timing was BTDC 30 degree, it was BTDC, At the time it dropped to 600. it was BDTC 20 degree

At 23 mins after engine start, the temp reached 80 degree Celsius, I pull the throttle, rpm rose from 600 to 1100, then the engine choke, I went on pulling, rpm didn't rise and a big "pop" from the intake. During the process, duty cycle rose a bit to 17% then back to 9%, EHA current dropped to 8.x mA, then back to 9.95mA. After I released the cable, rpm dropped to 300, ECU tried raising it back to 600, rpm dropped again, ECU tried again, rpm dropped, then engine stalled

I need a bit of time to digest the data, and will check if what happen between min 4-5 to the EHA current, likely duty cycle figures are normal, then decide what to do next. Next time, will ensure all data are captured on continuous format.

Any thoughts from folks are welcome.

Herrickmky

The continuous popping sound is from tailpipe
Engine started crispy when cold. After test, it won't start or needs a long cranking
The HV pin looks fine, at least in a much better condition than those contact points, I may consider testing it with another distributor cap
I don't quite get what you denote to "error code on timing". If you mean the ignition timing, I misread the number. In the new round of test, I think I read it correctly and wrote it in the post for reference

Cheers!

dolucasi

(1) In some early post you said there is an error code "ignition timing error". Please verify if that piece of information is bogus and should be ignored.

(2) There are quite a few things troubling about your readings, so not sure which one I should address, but I will address them in no particular order.

- Your O2 sensor readings. A proper reading is the voltage reading will cycle back and forth between 100mV to 900mV every 1-2 seconds. You did not report anything like that, so there is definitely something wrong there.
- Does your model have the biodegradable harness wiring? If so, you probably have issues emanating from that. This is very important, please check into it.
- Popping from intake points to bad timing or absence of spark and because of it unburnt fuel gets some sort of ignition when the intake valve is open at you get a pop from around the intake opening (throttle body)
- Popping from a hot exhaust is probably unburnt fuel igniting because it finds oxygen somewhere in the exhaust system and ignites.
- You never reported a cycling EHA current or Duty cycle after the engine warms up. That is a problem.
- And your ECU is forcing a high EHA current at some point and that is causing a very rich condition.

As a next experiment, after the engine warms up, unplug the EHA or simply disconnect the wire at the current meter. Tell us what happened to the running condition and the rpm's. This may throw a check engine light. Do not worry about that. In a normal condition this will raise the rpm's a bit but should correct the engine running rich condition that is forced by your ECU after warm-up.

Your ignition timing also does not look correct at different times, it should be 10 degree BTDC and solid around idle of 600-900rpm. It will only be higher BTDC if you raise the RPM and is also affected by the vacuum in the intake.

If you could address all the issues I raised and not produce more unrelated data, that would help. This will have to be a linear diagnostic, not a random collection of data. I know it is difficult from a long distance because sometimes days pass between comments/re-taking of data but this will help us focus towards a culprit in a organized manner.

I am confident your Fuel Distributor plunger adjustment screw is way off now. Chances of it being anywhere near where it needs to be is "zero".
So do not further adjust that screw to a point you can not even start the car. At that point you will be in even a bigger hole.

To see if you are somewhere near the correct adjustment point press down the AFM plate with the car not running. There should be about a 2mm free-play before you feel pressure. Tell us if this is true in your case. Remember, whatever you find out "Do not" mess with that Adjustment screw before you report on the result.

And most importantly patience is what you need at this point. And do report on the bio-degradable wiring Harness issue. That could be a serious problem.

Herrickmky

Hi, my initial response embedded in the quoted text for easier reading.

Cheers!

dolucasi

Oddy there is a 92 W124CE for sale around me. It is not running so dirt cheap. If the guy ever replied to me I would buy it. Perhaps I could help you with more direct knowledge. But I digress.

(1) TIming error code - That is your primary problem. Like I said before you need to resolve this before anything else. The timing signal indeed goes from the EZL to the MAS because that's where the idle controller resides for your model, then unto ECU, You would need an oscilloscope to look at that signal to figure out what's wrong with it. I still suspect you EZL is at fault here from all I have heard so far. This maybe causing all kinds of trouble with the ECU.
(2) O2 sensor - can you elaborate on what you said? What is the cycle frequency of this signal sweeping from 300+mV to 700mV? That by the way is less than it should swing from my knowledge and measurements.
(3) Duty Cycle - That just appears to be an error code. It is close to 10%, so that is:

10%: TPS (throttle position sensor), throttle fully closed signal
or (if at 2.000 rpm) no/false supply voltage to POT (air flow potentiometer)

Or ......
the ECU is railing the EHA current to near the max. I'm not sure what the max value for your model is. Mine is 20mA. But I know each model is different and larger engines are like 10mA.
Do you know your model's M104 max EHA current? You should find that out. I would not be surprised if the max for your car is 10mA under running temp.
Though your ignition-on engine-off value is 20mA from your posts and that is generally the max value at I-on, E-off.

Let us know how the car behaves when you unplug/disconnect the EHA.

BTW your idle appears to be fine now. It is not high like it was before and has the right behaviour when cold and warm. Not sure what fixed that. Or is it still unpredictable, sometimes high sometimes normal.

Herrickmky

Seems to settle at 1200 to 1300 rpm

Herrickmky

I managed to get an used EZL from a local scrap yard. Apparently it has sat on the shelf for a long time and there is no guarantee that it is healthy. I decide to give it a try. With all components remaining the same except the EZL, the result is more or less the same. the details are as follows:




The x axis ended at 30 mins. For unknown reason, the label from 16.5 to 30 were missing

During the process, I read the OBD I code on the fly, there is no code at all, not even the Crank Position Sensor error.

After the temperature reached 80 degree Celsius, I unplugged the EHA plug, The RPM dropped like a free fall and tended to stall, ECU intervened immediately to raise the rpm. I plugged the EHA connector back, the RPM resumed to where it was - 600 rpm. I unplugged the EHA plug again and not connected it back, After a single attempt to raise the RPM to 800, it dropped to stall

Wondering what trigger the sharp falling of the EHA current and duty cycle. The rich reading of O2?

Post test checking

• All spark plugs are covered by carbon
• Crank position sensor came back as usual

Next test
Tomorrow I'll unplug the ECU and test if the Crank Position Sensor is sending signal to the ECU

dolucasi

It is good to know that your timing error has gone away after the EZL change. Now we can safely diagnose other issues. At some point make sure you use a heat conducting paste after you are back to operating normally.

O2 sensor - please post a 20 second video of this after the car warms up, it certainly does not sound right, it should be sweeping from ~100mV to ~900mV EVERY 2 seconds in a working emissions loop. Have you replaced your O2 sensor lately? It is possible this is causing your issues
EHA current - It appears your FD lever is adjusted way too rich (or the O2 sensor loop is broken. I believe 10mA is your max current and the ECU is railing to it. When you disconnect it, instead of things getting better they get worse. Also next time you try disconnecting, disconnect the IACV first so the engine does not stall as it will sit at a high rpm like 1100 when you disconnect the IACV.

If you do not know the history of your O2 sensor, replace it now.

If you do have the history and believe it is a working unit, it is time to try to adjust your FD plunger back closer to where it needs to be, no more than 1/8 the turn at a time while your are monitoring the EHA current to see if you can center it to around 0mA. You will need to do this after the O2 sensor replacement. Make sure you are turning it in the correct direction, to lean the mixture, look up if that is CW or CCW. You do not want to go in the wrong direction.

What is strange is that the OBD or CEL does not trigger since your EHA current is railed. That is puzzling. Also when you unplug the EHA, in my model year that will trigger a CEL, I'm surprised you did not report such a thing. Very strange.

Also, how do you feel about your EGR valve loop? Any chance it is stuck open? That could be an issue too. Read up on that. My car does not have an EGR valve (pre '90's did not) so my experience there is limited. Generally the EGR valve get's plugged with crud not the other way around (stuck open) but who knows.

Herrickmky

Some initial response in the quoted text

dolucasi

CEL is Check Engine Light. Sometimes referred to O2 sensor signal.

Yeah the O2 sensor output is no good. Change it to see if you can get the expected signal.

If you are still getting timing error from the ECU that is not good.

When you say you are getting a timing error, what is this like. Is that the 16 pin connector diagnostic port?
Can you give details? Is it possible you are misinterpreting this?

- Cheers!