Hi all,Recently I bought a non running Euro Spec 88 300CE. I now have it running. ​​​​​​​When I start it, it idles about 600 rpm, after 5-10 seconds goes to about 1000, then to about 1300. Revving does not reset it, turning off will, but cycle above repeats.​​​​​​​I have replaced Bosch non- resistor plugs, distributor cap, fuel filter and temperature sensor at rear of head with new. I had on hand a new Uro brand ovp relay, that normalized idle, but cold start injector did not work. Swapping a better brand used ovp relay activates cold start injector, but back to high idle.I have a lot of good used parts on hand from years of parting out these cars. I have tried good used fuel distributor, eha, ezl, coil, ecu with no or little change. A wierd thing, if I disconnect the vacuum line from intake manifold to ezl, idle drops about 3-500 rpm, seems to rev normally. When it is idling, high or normal, I can hear a very faint miss. Yesterday I took it for a drive. When I accelerated hard, it would miss and jerk just before shifting (automatic transmission).​​​​​​​ All that said, anyone have any idea what the problem is, what to try next?Thanks

 

Sounds like you have a lot going on there and have multiple issues.
I would chuck that URO OVP pronto. Usually their parts are not a good fit for particular model years etc. Been there myself with simple stuff like antenna rubber seal, etc.

(1) How many miles on the engine/car?
(2) So does it idle higher rpm upon cold start? How is that behavior?
(3) Were you describing hot start idle? Namely the rpm slowly creeps up. Please verify this.
(4) After it gets to the 1300 rpm, what happens when you disconnect the plug to the IACV? What happens when you plug it back in as the car is running?
(5) Your running issues most likely are unrelated to the high idle but we will find out.

 

Hey,yes, URO OVP Relay gone, I don’t trust their parts, just happened to have it.About 200K kms on car and engine, engine was swapped from a same year car a few years ago by previous owner, don’t know why.Definitely idle speed creeping up on hot starts.Cold starts still difficult, doesn't idle well at all on cold starts, stalls. On cold starts only starts without any gas pedal added.I haven't tried unplugging the IAC, will do tomorrow, but I had tested it and it seems to work properly with 12 volts applied.Thanks

 

Like I said, sounds like multiple issues. We are unplugging the IACV not really to see if it is working, we are trying to find out what state it is in at 1300rpm. If it does not change at all you know it is receiving 0V. I'm pretty sure it is working because your idle is drifting upwards.

Cold start must be yet a separate problem. We will have to tackle that separately.

I wonder if you should question the quality of the swap and if they got all the harnesses connected properly.

Sooner or later you will also have to do some EHA current and/or duty cycle measurements. I would start with the IACV unplug followed by plug. A working IACV closed loop operation would cause a near stall or stall upon plugging back in.

- Cheers!

 

One more question, did the '88 124's have an economy gauge? W201's did. Where is it sitting at if you have it. Full scale is 17 inch-mercury which is the required minimum for these cars in neutral gear.
Lower may indicate vacuum leaks or engine running issues like timing/low compression/etc.

 

Yes, it has the vacuum / economy gauge. That is behaving as it should, ie pegged low in the black idling, towards middle when revving, etc.

 

Further updates:When cold (ie overnight), it takes several tries to start. It runs a few seconds and dies, pedal doesn't help. When it does keep running, revving causes backfire through intake. Idle speed increases as it warms up, about 1000 after a few seconds, then to 12-1300. Unplugging the IAC makes absolutely no difference. I do know the cold start valve is working - have pulled and tested when cranking car. Also, car has fresh premium gas.

 

Good that your vacuum appears to be healthy.

(1) Backfire from intake points to incomplete ignition either due to an ignition system problem or fuel mixture being too rich and flooding the intake. I would put a strobe light and see how the timing is during warm up and operating temp and if you are getting steady 10% BTDC and not a jumpy one even during cranking.
(2) Engine should start on a dime cold for the M103 engine given the CSV fires for 1-2 seconds, fuel enrichment is there, and the proper fuel pressure is present.
(3) No change in idle rpm when IACV is unplugged means you have 0V at the IACV like I mentioned in the previous post. You can measure it (with it plugged in but I'm pretty confident).

On item 3, it sounds like IACV is receiving 0 volts all the time and the rpm is changing based on the operating conditions of coolant temp, engine timing (based on comment about your unplugging the vacuum EZL seems to change rpms). etc. This would also explain the steady rpm rise during the engine heating up.

So you can verify this by measuring the voltage by sticking a couple of thin wires in the connector or wire wrap around the male side of the connector etc.
Or you can verify by disconnecting the IACV and cold start it and see if the behavior is the same as when it was plugged in. Your choice.

You should focus on this IACV before tackling item (2) above.

I would question the wiring between the IACV and the ECU since the engine was swapped and you already swapped in different ECU's without success.
You can measure the wire resistance between the connector at the IACV and at the ECU.

 

Been busy with other stuff, a bit of time on the car yesterday. So, the IAC circuit is getting full voltage. The IAC works if I apply current directly to it. When I connect the plug to the IAC, leaving just enough room for multimeter leads, there is zero current reading.
I checked the terminals in the plug and they are tight.
When car is running, and I apply direct current to IAC, the engine revs higher.
​​​​​​​I'm puzzled.

 

You have some discrepancies in your statements above:

DLL>>> So, the IAC circuit is getting full voltage

but later in the post:

DLL>>>When I connect the plug to the IAC, leaving just enough room for multimeter leads, there is zero current reading.
I checked the terminals in the plug and they are tight.

I'm going to assume is first statement is a typo.

It is pretty clear your ECU is not attempting to control idle and either is in

(1) limp mode
(2) There is a connection issue between the IACV plug and the ECU (not very common but possible)
(3) ECU is busted (not very common but possible)

I would focus on verifying that you are in limp mode first.

One way is to unplug the EHA connector when the car is idling. If nothing changes, you are indeed limp mode.

Please report on that quick experiment.

-Happy Sunday

 

I'll check the eha, but, my previous comment is strange but accurate. The terminals for IAC get full voltage disconnected, but connected a reading of zero on the IAC terminals

 

Just tried IAC test, disconnected engine idle drops low, nearly stalls. Re connected back to high idle.Tried same test with O2 sensor, same results

 

Sorry, typo above, disconnected EHA and idle dropped to almost stalling, reconnected back to high idle

 

Also, tried unplugging potentiometer, absolutely no change to running engine. I don't know if related, but car has ABS light on.​​​​​​​That made me think OVP relay, but, have tried several (red top dual fuse) without change. ​​​​​​​

 

Let me give all your inputs some more thought but... Clearly the connection from ECU to IACV is not the problem. Also your car is NOT in limp mode.

ECU is driving 0V to the IACV meaning it is in some mode where it thinks the car is not idling.
Did you check to see if your throttle linkage and microswitch are operating properly. I do not remember if we checked that already. The microswitch is what "orders" the ECU to put the car in idle mode.

- Cheers!

 

Some updates-I started thinking about the potentiometer, test the ohms, didn't get good readings, swapped, adjustments to specs, still no difference. ​​​​​​​Today, I started thinking about fuel pressure. I don't have the fittings to adapt my gauge to the M103, so tried the 40 second volume test.​​​​​​​I unhooked the fuel regulator return line, and put it into a bottle marked for 1 litre (in 40 seconds).​​​​​​​When I turn on the key, I only get that initial surge of fuel (I did test cranking over, got strong flow).That makes me suspect one of the fuel pumps could have failed?​​​​​​​Will probably pull and test pumps sometime in the next few days.

 

Hi guys,
I haven't followed this thread to every letter and I don't get all the acronyms but I had a real issue with my (UK) 230 TE (gas engined, estate).
The first was that my wife was stranded as it would not start. I got there and sprayed some brake cleaner into the intake and it started easily - for a few seconds until the spray ran out.
So it wasn't getting fuel. I found out how to hot wire the fuel pump (a simple figure of eight copper wire around two terminals on the fuel pump relay. That got me home. On looking very (!) closely at the fuel pump terminations I could see a crack in a solder joint.
So I re-flowed that with solder and it fixed the issue. About a year later the car was getting more difficult to start, it would cut out sometimes and the idle speed was all over the place. I replaced the throttle cable, no difference whatever.
So I then removed the fuel pump relay once again (on UK cars it's right behind the battery) and on closer inspection could see more cracks in the solder joints on the output terminals - i.e. where the PCB gets connected to the pins that stick out of the bottom.
I solder-sucked ALL of them dry, used plenty of flux and re-soldered them all and ever since the car has started and idled perfectly - like you sometimes can't tell if the engine is running or not except by the rev counter.
I don't know if this will help but it sure did sort mine out. And it cost me probably less than 5 pence worth of solder and flux and power for the soldering iron.
all the best
Neil (in the rain-sodden UK)

 

Hi Neil, these are not similar symptoms but it sure sounds like your Fuel Pumps are drawing too much current and busting your solder joints. I would get that checked. Each pump should draw about 10A when running. Seems yours is drawing more and not just quite enough to trip fuse/relay. If your pumps are over or nearing 100Kmiles, they need replaced. That is with a super clean fuel system, mileage could be considerably lower under certain conditions like dirty fuel.

Cheers from a rain soaked California!

 

Just remember one thing about the potentiometer. It's functionality is limited to cold operation mostly. It let's the ECU know what the position of the AFM plate is and how fast it is moving so that fuel can be enriched properly on a cold engine. That is because the engine air/fuel mixture needs to be something other than the lambda=1 in cold. And the colder the engine the more enrichment is needed. So if you had complained about the car stumbling under acceleration while cold I would have had you look at that. Sure a potentiometer could throw the ECU into tailspin if misbehaving but that possibility is near zero. You could have just tested yours in place and would have noticed some discontinuities here and there as it will be worn at 200K miles. Nearly 100% of the cars on the road today with 200Kmiles (including mine) will have worn potentiometers an none of the owners will be aware of that fact because they can not even tell the difference.

One thing you do not want to get into is the cycle of swapping parts unnecessarily as that itself can cause issues. At least if you are going to do that make sure you do not swap in aftermarket low quality parts as that will make you chase yet other issues and if you do not "observe cause and effect" swap your original part back in.

Anyway, I could have saved you the time with the Pot, had you questioned it.

You did not get back to me on the microswitch and it's operation. After that we should also check the Throttle plate switch.

You said your engine was swapped with another engine of equivalent mileage. Was than an '88 engine or later? It would not make sense to swap in another '88 or early '89 engine as they have a known CAM and oiler defects. Most of those will be toast by that mileage unless taken care off. You can tell by taking your cover off and looking at the cam and rockers or read the engine serial number and going down to your Dealership and asking if it's date of birth is pre or post March-89.

I am still suspecting something was not quite right with your engine swap. Most likely in wiring. Or during the swap the ECU may have gotten zapped if not disconnected prior to the swap.
Can not remember if you tried an ECU swap already. The IACV receiving zero volts means the ECU is not controlling the IACV at all. Need to question: wiring, ECU, microswitch, TPS for that.

 

Hi, yes, microswitch fine. I don't know why the engine swap was done in the first place, previous owner, but 88 to 88, A Japanese market 300ce engine into this Euro 300ce. I have the donor car. The potentiometer, cold start takes multiple tries, runs a few seconds and dies. It doesn't run well enough to drive at all until warmed up. The meter readings were way out and would not adjust properly (7, or .7 (I forget the decimal point offhand), so swapped it, adjusted, got correct ohm readings, but no improvement in car running. I have also swapped ECU. I have a lot of good used OEM parts on hand (I've been working with, parting out these cars for a while). I only keep known good parts. I don't like most aftermarket parts too.

 

After changing and adjusting the potentiometer, after it warmed up, I took it for a test drive. At moderate throttle drove OK, seemed OK on full throttle until about 4K (or just before upshift), then started bucking and stumbling, as before

 

Like I said DLL, the Pot has almost nothing to do with running issues when hot. Your mixture does not get adjusted by the ECU based on the input from the Pot.
As a matter of fact the only time the mixture is adjusted is on a WOT (wide open throttle) and that mixture adjustment is relatively minor from my measurements in the grand scheme of things.

The cold start issues are also unrelated to the pot. For that most likely your CSV is not firing and after it starts the ECU is not adjusting the mixture (this one could be AFM pot but you already swapped and concluded it is not your pot)

I actually have an analog EHA meter installed in my car and have also posted graphs on the W201 forum a year or two ago of the EHA current (AKA duty cycle) measurements. You can check them out to give you an idea.

Since you already vindicated the ECU and the microswitch, you are down to the TPS. Make the diagnostic measurements there (do not swap it though) and see if it is working at all.
It is like a slide switch with 3 pins and 3 positions. Closed throttle, (2 pins shorted), throttle open but not WOT (all pins open), WOT (the other 2 pins shorted).

 

Thanks for info on the Pot.The cold start injector is (at least was) working, I tested it by removing, and watching while cranking car, it sprayed fuel while cranking.​​​​​​​To test the TPS, just as simple as it sounds? Access the connections, short 2, then 3 wires with key on? ​​​​​​​Thanks​​​​​​​(Nice weather on Vancouver Island today, took my 500SL out for a rip - to refresh myself how a properly working old Benz feels!)

 

Sounds great! Yes the TPS has easier to access connections up above near the IACV I think for ease of measurements. Do not quote me on this but it goes something like this:

1.....2.....3
-------- 1 shorted to 2 , Throttle plate closed
------- 1, 2, 3 all open, Throttle plate open
------- 2 shorted to 3, Throttle plate wide open

I may have given the pin numbers incorrectly so read up on that please.

If you are good with the multimeter, I would recommend reading your EHA current during cold start (should be plus 20mA with ignition on engine off) and Something even higher after you start the engine. It should gradually come down to near zero an start oscillating near zero but hours seems to be not doing that.

 

Yeah I guess that's possible - I just put the condition of the joints down to age and being constantly shaken - the rest of the electronics in the relay looked squeaky clean and none of the tell tale smell of cooking electronics which I am very familiar with from other interests (amp building). The car has done about 120K miles. Thanks for the thought !
Neil