dolucasi

Like I mentioned prior rufrob, you have multiple issues and some of these are unrelated.
You are correct the IACV should not cause running issues when not in idle.
That is yet another problem.

On your idle issue, just remember this is a closed loop idle control. In a system like this there is always a "steady state" condition that everything is in working order and the sensors (in this case your rpm reading, control signals (throttle plate switch, micro switch), and the IACV (the actuator) as well as the controller ECU have to be in working order.
If one or more of these are malfunctioning the closed system instead of stabilizing at a desired idle of 750rpm's can go into an oscillation like you are seeing.
Basically the ECU sees the rpms as very high and tries to rail the IACV in the opposite direction and if the IACV is not responding properly the signal will be overshot. And there you go a classic "mono-stable multi-vibrator" condition is created.

Let's see if cleaning the IACV thoroughly will resolve this. Let us know how that turns out but swapping in another known good unit is always an option.
When you are done cleaning, shake the IACV (rotationally) in your hand and make sure it is rattling freely and that the rattling does not come and go indicating it is being stuck occasionally.

rufrob

Thanks

I tried removing the IACV last night but had to stop when I couldn't find some tools.
Again the hoses fuel hoses etc much come off and the hard to reach air hose from IACV to the base of the air box.
I've taken the FD assembly off so many times I can do it eyes closed.

rufrob

Got the IACV off and yes it's stuck 1/4 open. Looked clean though. I sprayed some carb cleaner in and some brown stuff came out.
I'll soak it best I can overnight and see what tomorrow looks like.

dolucasi

It may or may not be stuck. When no voltage is applied you will see about a 2mm slit opening. This is because if your OVP dies the car can still idle at a fixed but high rpm.
The key is, does it rattle? If it does not it is stuck. I have 2 IACV's in my parts shelf. One my original and another one from a JY car. Neither one of them rattle when shaken violently.
Both look super clean inside. One does not normally get fuel or oil deposits in an IACV and it appears does not take much to get stuck after 30 years.

Key is when you apply solvents, and when wet does it rattle for a little while and stop rattling when dry? If so, you have to keep flushing.

- Cheers!

rufrob

Surprisingly it didn't take much cleaning to get the rattle. The little door slides easily now.

dolucasi

Great! Let us know how the idle does after you re-install. Hopefully one more item can be checked off.

rufrob

Reinstalled the IACV
First

3-2=0
6-6=12.30
IGN on
3-2=3.65
6-2=12.06
Eng on@2000rpm
3-2=6.98
Then I accidentally erased the measurements
The fluctuation range and severity lessened
When warmed up the idle was very low and occasionally stalled.
I'll let the engine cool and test it again tonight.

Benz here wants $80 for the heater control valve.

dolucasi

So at cold it was idling at 2000rpm? For how long? Until it reached 85 degrees C.

Maybe report on the idle from cold start. Like this:

cold (20c) - xxxx rpm - rpm range of cycling
40c - yyyy rpm (first tick mark on gauge) - rpm range if cycling
60c- zzzz rpm (second tick mark on gauge) - rpm range if cycling
80c- www rpm (3rd tick mark on gauge) - rpm range if cycling
85c- qqqq rpm - I think we know this one, it goes really low and eventually stalls

Alternatively, take a long video (probably 2-3 minutes) from start of the dash. And post it on youtube and post a link to it.

rufrob

Ign off
3-2=0
6-2=12.27
IGN on
3-2=3.63
6.2=11.95
Engine on
3-2=6.93
6-2=13.86
High idle 2000rpm until 85 degrees.
Warmed up fluctuation to stalling
3-2=6.18-6.24
6-2=12.38-12.50

I'll post a video shortly

rufrob

Same low idle after disconnecting the IACV

rufrob

At cold start the rpms are 1800 then goes up to 2000 from about 80degreesC.
Just before the fan kicked on the rpm decreases then start fluctuating to a low idle recovers a few times then stalls.
Restarts to 2000rpms then drop to a low idle. It recovers if I touch the throttle but bogs when trying to rev.
Guess the IACV needs more cleaning?

rufrob

Now it 80 degreesC
About 950rpm
3-2=6.85
6-2=13.75
But it won't rev freely. Bogs and backfires when revved.
At 100 degree and 1000rpm
3-2=6.88
6-2=13.81

dolucasi

I'm not sure if that is a sticking IACV. Firstly your duty cycle is not riding up and down at operating temperature. So it never get's into closed loop mixture control. That is problem number one.
That means your mixture is whatever you adjusted your mixture screw is (lately). Which is also bad because we know you adjusted it without monitoring duty cycle or FD pressures. Hopefully my memory is not failing me here.

Let us first diagnose your idle. Can you stick a couple of copper wires into the IACV terminal with it plugged in please?
Once again from cold all the way to warm temp please report in the voltage between the terminals with your meter in "DC" mode.

Report the IACV voltage at various coolant temp levels using the coolant temp sensor in the cluster.
Again in each tick mark of 25c (cold), 40c, 60c, 80c, operating (100c?, BTW which is a bit high just idling for a few minutes).

This will tell us if the IACV is stuck or whether the ECU is telling the IACV to open all the way.

Do not need the pin 3-2 readings any longer. It is 70% with no idle (correct) and 50% at cold (correct), and stuck at 50% hot. So this is a separate problem.

190Efan

With the way the car knocked so badly under both start scenarios, I can't help but wonder about the quality of the gas that's currently in the vehicle? Bad gas can cause that type of severe knocking. Sounds to me like there is likely multiple things going on. Changing the mixture was a really bad idea that's probably made things worse as well. The grinding before the cold start sounds to me what my car was doing and that resulted in replacing the EHA. My car starts and runs fine now. You might also want to contact the MB Classic Center to find out what the original mixture setting was when your car left the factory. That; will further help to understand where your car is at now.

rufrob

The gas is fresh premium.
I doubt the dealer will tell me. This is a Japan only spec. I'll check anyway.

rufrob

7.72v cold idle at 2100rpm
7.79v@40degree
7.80v@60
7.80v@80
4.90-5.00v @82 degrees idle drops to 1000rpm.
Still wont bogs and wont rev.
Fan kicked on at 100 degrees 4.90-4.98v.
Btw I've been using DC volts for checking terminal x all this time.

dolucasi

So we sort of know your IACV is not sticking (at least now during that measurement). Those are in line with a working IACV and the voltage will be 4.2-4.8 with a normal idle (750 rpm).
You idle controller is forcing this high idle during warm up. It also vindicates your system from vacuum leaks, sticking throttle plate and linkage, etc.
BTW, yes all measurements are done in DC mode for the car diagnostics as all signals are either pulsed square wave but we use average voltages (not RMS which measures the AC component) or they are true DC voltages.

Now, please verify the following:
(1) Has anyone swapped in a wrong ECU for this car? You may need to check the part number for this and google it on the WEB. Putting in a 2.6 ECU would have this sort of behavior.
(2) Have you checked the micro-switch and the throttle plate switch for operability already. If not we will work on these next.

Your ECU is also not regulating for air/fuel mixture at operating temp. So after we verify #1 and #2 above, we will tackle that next. BTW, do you have an OBD-1 code reader (the one with flashing LED's) or does this 2.5L already have a built in code reader (the diagnostic box on the fender by the battery). Thought this is Japanese built so it should have been RHD, but it is not, the video suggested LHD. Maybe all 2.5's were LHD, they only made 500 of them I think)


- Cheers!

190Efan

Fresh gas rules out the bad gas possibility. You need to check the original idle setting with the MB Classic Center because the local MB dealer is less likely to know that. You can contact the MB Classic Center online.

190Efan

Either a wrong ECU or an incompatible aftermarket ECU. I don't know if all of the 2.5 16vs were LHD or not but I do know that 5,700 2.5-16vs were built. It was 500 EVO 1s and an additional 500 EVO 2s were built. The 2.5-16 vs is still the rarest W201 outside of the EVOs.

dolucasi

I see. So the 2.5's are less rare than the 2.3 16V. I did not know that. I thought the opposite. Good to know., Thanks 190Efan.

rufrob

Thanks again

Who knows this cars history.
Glad to know there aren't any major vacuum leaks. I sprayed brake cleaner at the hoses to the injectors and occasionally it would stall at the rear/right one which has some cracks. I ordered from the US but was NLA.
I was told by a friend who has a 2.3 all Japanese 2.5 were LHD automatics apart from the uber rare EVO 1&2. No sure how many were made but I'm quite sure much fewer remain.
I'll check the computer PN tomorrow. As well as the micro switch at the throttle plate.

rufrob

Might you know the pn and or Bosch pn for the 2.5? Is it the same as the 2.3 and 2.5 16 EVO?

dolucasi

Just search for: 2.5-16V Evolution ECU

in google and a whole bunch will come up. I clicked the first one and got:

Engine control / unit ecu motor Mercedes Benz 190 E 2.5 16 V EVOLUTION 006-545-0232 (MB) Bosch 0280800230

Do a sanity check with a few others and see if they are all matching and you have the numbers. Check against yours.

- Cheers

dolucasi

And if yours is a different number, do the reverse, google search for your part number and see what engine is it for really.

- cheers

rufrob

I spent the entire afternoon painting the garage where the car is parked.
There is no micro switch at the throttle plate only on the linkage. I guess that's what you mean.
When checking I discovered my dumbassery. The big seal at the throttle plate wasn't seated properly.
At first it did the same bogging and high idle.
A few restarts the idle is still high but suddenly it started revving freely. No more backfires and bogging.
It keeps the high idle at 2000rpm even when hot.
Occasionally it will idle properly.
Hot restarts ok
But cool restarts require long cranks.
The ECU appears to be correct.
Light at the end of the tunnel!!