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Discussion Starter #1
Hello Guys. What I am describing seems to be pretty common with these cars but I have some additional observations that s why I m opening this thread.
I drove my car abt 3 days in hot weather and never experienced a problem. the second day I started the car. it starts normally and immediately but when started it felt like the idle control valve kicked harder than usual(Idle got up faster and for a longer period). problem is that while driving and AC on, once I released the throttle and press the clutch pedal the Idle drops to normal than surges to abt 1300RPM than drop-down again(rpm bouncing) and the engine feels like its gonna stall (it stalled 2 times when AC is On). same problem when AC is off but it doesn't stall.
one more observation is that when I m running downhill with foot off the accelerator the car feels like it's not decelerating normally as it should. it feels like the fuel cut off is getting interrupted somehow and I can feel a little shake (like engine braking is releasing and latching randomly).

A) My first thought was the deceleration microswitch but it tested ok and its connection to ECU is ok as well. also, the throttle linkage is all good.
B) I have a spare ECU (other S/N than the installed one, a newer version), I fitted it, well I can't say that it solved the problem 100% but the idle drop and surge are not that noticeable, and no frequent stalls. so things got improved but the problem source is obviously still existent.
Cars Idle fine no changes in idle after the problem occurred. it also pulls up like a lion without any power flaws.

Does an ICV cause this sort of problem? or maybe the Airflow potentiometer? or a simple vacuum leak?
I need your advice guys where to start from as in my country mechanics only change parts till the problem is solved.
I'll try to make a video today after work for a better explanation.
Thank you so much.
 

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Discussion Starter #2 (Edited)

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Vakuumleak and airmasssensor/potmeter have give med this failure.

Sent fra min H8324 via Tapatalk
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I have a few questions perhaps you can answer:
(1) Is this a M103/M102 engine? Rest of the questions assumes "yes" to this question, ignore the rest if the answer is "no"
(2) Why is it idling at 500rpm? It should be 750 +/-50 rpms
(3) Why is your coolant temp below 80c? You must have a faulty or incorrect thermostat in the car. The full emissions does not kick in till the coolant temp hits 80c.
(4) Please check the date code on your OVP assuming this is an M103/M102
 

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Discussion Starter #5 (Edited)
I have a few questions perhaps you can answer:
(1) Is this a M103/M102 engine? Rest of the questions assumes "yes" to this question, ignore the rest if the answer is "no"
(2) Why is it idling at 500rpm? It should be 750 +/-50 rpms
(3) Why is your coolant temp below 80c? You must have a faulty or incorrect thermostat in the car. The full emissions does not kick in till the coolant temp hits 80c.
(4) Please check the date code on your OVP assuming this is an M103/M102
Hi. This car was originally a 200 carburator with m102. And engine was swaped 20 years ago. So lot of things are mixed up together. But all was workong like a swiss watch for years and never gave a problem.

1- now it s an m102 engine. A euro 2.3L version with dual row timing chain.( I suppose m102.985)

2- i m driving the car since 1995 and it always idles at 500 or 550. Maybe because it s a manual transmission. I may say that after the problem occured the idle slightly decreased maybe -50 and when engine warm i can listen to that +-50 idle fluctuation now (feels like an invisible vacuum leak)

3- my version of ke jetronic doesnt have o2 sensor or emission control it even doesnt have the duty cycle measutement pin in diagnostic socket. I replaced the thermostat years ago and couldnt find the original one. This one is a 80°c.

4- the ovp relay has been replaced many times randomly by checking some used ones that works so i dont feel like the code date is accurate here. It the the black one with single fuse.

I would like to address a little question here: i found out that the original ECU was for the 2L engines. the replacement one is the correct for 2.3L. but i notice that with original ecu after releasing the gas pedal rpm used to drop a lot faster then with the new ECU as it feels like they drop slowly. I am confused which one is the correct behaviour.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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Glad I asked the questions. You have a lot going on there with a car that is way off from a US spec car.
So I'm not sure I can help you with all these differences and replaced engine parts on yours.

One thing I can tell you is that the idle speed is NOT related to your manual transmission.
I have had my car since 1989 (new), it is also manual transmission. It has always and still idles at ~725rpm.
All the manuals and books I have read mentions rpm should be 750rpm (+/-50). This is for an M103. I believe M102's idle is even slightly higher (I believe 800rpm +/- 50)

What is shocking is even at 500rpm your vacuum gauge is pegged to the stop, that is great.

I would still check the date code on that OVP. At least you will know when it was manufactured even if you know the actual operating life maybe shorter.
Hypothetically let's say it turns out to say 32/99 or 32-99 on it. Would you trust that OVP that has been in service for possibly 21 years?

I am not saying it is definitely your OVP but the behavior makes it suspect. Intermittent OVP failures will cause idle surges and unexpected stalls, especially with manual transmission cars.
I have witnessed this myself. Now I'm not sure about a non oxyen sensor car's behavior.

It is normal for the RPM's to drop slower than faster. This is because the ECU's generally have a 1+ second delay before they completely cutting-off the current using the EHA.
Is the ECU that you swapped in also from a car that does not have an oxygen sensor? Certainly mixing that will give you trouble.

An Jetronic engine without an oxygen sensor is another beast. If your EHA/FD is not in perfect tune it would be hard to adjust fuel/air ratio. How would you do it without a tailpipe sniffer?
 

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Discussion Starter #7
I have tried to swap the OVP with a known good one and no changes at all.
the ECU was given to me years ago from a friend. so the status is also unknown. but the difference in the rpm drop seems related to some fuel maps change between both ECU as it feels like the original one cut the fuel 1 or 2 seconds before the replacement ECU.
I can feel something strange that happened after this problem which seems like I lost the fuel cut off function on deceleration when running downhill. that s why my first culprit was the throttle microswitch but it tested ok (switch and circuit) will a Vaccum leak lead to that kind of bad deceleration feeling?

for the Mixture and EHA Adjustment, I did it using an old method by slightly pushing down the airflow meter plate while monitoring the idle quality. if improved then I enrich the mixture and the reverse is correct. believe me, the car runs like a beast it may seem overpowered for an m102 I even had to change my diff ratio as it used to spin the wheels on 2nd gear. CO emission is 0.8 which is passing the emission test in my country.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I would probably start by measuring EHA current on yours. See what the ECU is doing to control the air fuel mixture. I suppose it should behave similar to a oxygen sensor engine.
Also monitor the IACV average voltage and see what is going on there. Is it the ECU causing the low and unstable idle? Or is it something else?
 

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Discussion Starter #9
While ECU is unpluged or ICV unpluged the idle raise for abt 1200rpm then stabilize to 5000+- when ecu is plugged.
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I think you meant 500 when plugged. That is normal behavior (1200rpm when unplugged) . So the ECU is forcing 500rpm for an unknown reason.

Any chance that ECU came from a M103? Not sure how the ECU determines what the RPM is but 500rpm * 6cyl / *4cyl = 750rpm.

Or are you actually running 750 rpm and the gauge is telling you it is 500rpm? Is your RPM's really correct running down the road at 60mph in 5th gear?

Do you have an independent engine analyzer that will tell you what the real rpm's are?
 

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Discussion Starter #11
yeah sorry, I meant 500 when plugged. as per serial number, the ECU comes to form an m102.962 engine I guess it was used on a w201. my replacement ECU is for 2.3L m102 engine and there is the same behaviour on the RPM. I don't have an independent engine analyzer in order to check. but I can tell the idle is smooth.
in the meantime, I m not willing to investigate the idle issue as its running like that since years. but I want to solve the problem that suddenly appeared form nowhere.
could it be a the ICV? sticking somewhere? does it cause this kind of problems?
 

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89 190E2.6- 5-speed Manual, 95 E320 Sportsline-sold, 2001 E320 4matic Wagon-sold
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I would not be happy with a 500rpm idle but that is up to you.
In the past perhaps two wrongs were making the idle right. Who knows.

The proper diagnosis in your case is to take a measurement I suggested earlier and maybe one more.
Measure your IACV voltage and see if it is stable.
Measure your EHA current and see if it is in spec.

Not seeing your car personally hard to give you advice from 1000's of miles away however your symptoms are exactly the same of an OVP (or wiring from the OVP) cutting in and out.
When it cuts out the idle will surge to 1200-1300 and the ECU is no longer functioning.
And when the power comes back on as the ECU is waking up most of the time the car would stall, or at least drop to near zero before it self corrects.
Also the EHA fuel cut off function will be gone as the EHA current will be zero at all times as long as the OVP is cut off.

I was also suspicious of an IACV sticking and took it out and bench tested it with a variable power supply. Found nothing wrong with it and put it back in.
Still not satisfied swapped in a IACV from a junk car and same difference.

After chasing my tail for 3-4 months it turned out to be the 10 year old OVP. Some in this exact same forum gave me advice on the diagnosis.
Look for it under my user name and you will find it.
 

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Discussion Starter #13 (Edited)
I am waiting for tomorrow so I can have time to begin the tests for the ICV and EHA. I m also planning to do some Vaccum leak test as the problem appeared after driving the car for a long period in surprisingly hot weather in my area(maybe some hose got a crack due to heat).
by the way, I am guessing that the replacement ECU is making the car run richer than before that s why it is performing better in my situation and rpm are slower to settle
i always had poor performance on my old ECU till the day I adjusted my EHA a 1/8 turn and all was good since.

what am I supposed to see as a current variation at the EHA as the system doesn't have an Oxygene sensor so no closed-loop I never found any information concerning this system on euro cars without Lambda but I know that they exist? maybe the EHA just richen the mixture by reading the output from the airflow potentiometer and WOT switch.
 

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Correct.

The oxygen sensor just time averages the mixture so that the FD is centered for a given condition and it re-centers the mixture based on oxygen content. So if things go off-kilter over time with the emissions system one does not have to keep tuning things like you are having to.

It takes 2-3 update cycles (2 seconds each) to reach that average. So basically 5-10 seconds with the oxygen sensor loop.

So the oxygen sensor will have very little effect in on-demand fuel enrichment. All the other sensors do that (AFM, AFM pot, throttle switch, etc ,etc)

So you are just missing that "averaging" feature and the ability for the system to self adjust.

If you are interested in reviewing how the EHA current (thus the FD fuel enrichment and leaning), I posted that on the W201 forum with some graphs. Look up my username and something like "how does EHA current behave anyway?"
 

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Discussion Starter #15
Correct.

The oxygen sensor just time averages the mixture so that the FD is centered for a given condition and it re-centers the mixture based on oxygen content. So if things go off-kilter over time with the emissions system one does not have to keep tuning things like you are having to.

It takes 2-3 update cycles (2 seconds each) to reach that average. So basically 5-10 seconds with the oxygen sensor loop.

So the oxygen sensor will have very little effect in on-demand fuel enrichment. All the other sensors do that (AFM, AFM pot, throttle switch, etc ,etc)

So you are just missing that "averaging" feature and the ability for the system to self adjust.

If you are interested in reviewing how the EHA current (thus the FD fuel enrichment and leaning), I posted that on the W201 forum with some graphs. Look up my username and something like "how does EHA current behave anyway?"
Hello. I will look for your thread for sure. Today i was free and i did some tests. The AFM Pot. seems to be out of calibration maybe this is the cause of the slow idle but no dead spots while depressing the AFM. When measuring ICV voltage it is always stable around 5.35V. but the strange thing was that yhe voltage is dropping to 0 and the icv is behaving earlier then it should be when releasing the throttle which result in that idle bouncing and stalling. This lead me to yhink abt thr throttle switch. And tadaaa: IDLE and WOT contacts are both dead. I manually grounded the idle contact and it worked immediately no more idle bouncing and engine dont stall even with AC on. I managed temporary to hook a wire from the fuel decel cut off switch to the idle contact in the throttle switch and it worked like a charm. It seems that the WOT cobtact was dead long time ago tho because no change in the behaviour on full throttle.
 

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Discussion Starter #16
Hello. I will look for your thread for sure. Today i was free and i did some tests. The AFM Pot. seems to be out of calibration maybe this is the cause of the slow idle but no dead spots while depressing the AFM. When measuring ICV voltage it is always stable around 5.35V. but the strange thing was that the voltage is dropping to 0 and the icv is behaving earlier then it should be when releasing the throttle which result in that idle bouncing and stalling. This lead me to think about the throttle switch. And tadaaa: IDLE and WOT contacts are both dead. I manually grounded the idle contact and it worked immediately no more idle bouncing and engine dont stall even with AC on. I managed temporary to hook a wire from the fuel decel cut off microswitch to the idle contact in the throttle switch and it worked like a charm. It seems that the WOT contact was dead long time ago tho because no change in the behaviour on full throttle.
 

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Sounds like you have a few things to chase down with your electrical actuator/sensor wiring.
I was suspecting that a few wrongs were making things barely work, and this appears to be the case.
Let us know if you have specific questions on expected behavior.

Look into one more thing, I have read somewhere that certain non-US models have an adjustable idle speed.
I may be mis-remembering.
See if this it the case with your swapped engine.
 

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Discussion Starter #18
I guess the only remaining issue other than the throttle switch is the AFM pot calibration to get a higher idle however my idle seems to be smooth tho. While driving at 130Km/h. My rpm is at 2000.
What i really need to read about now is the procedure for replacing the throttle body knowing that the rubber boot is not available as new in my country. I dont know if it can be removed without beeing cracked after all these miles. I would like also to thank you for your assistance.
 

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130KM/Hr is roughly 80mi/Hr. At that speed I'm at ~3000rpm in 5th gear with a 3.27dif ratio. Yours could be lower (3.07 or 2.87) however, I believe your Tachometer is not correct in any case.
You can check your diff ratio that is stamped on it facing the rear of the car.

So this explains your low/not low idle.
 

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Discussion Starter #20
I changed my diff 2 years ago from 3.42 to 3.27.
So what can be giving a wrong rpm reading? I believe If it was the Crankshaft position sensor this would be leading to a ton of other problems. Maybe the gauge itself is defective.
 
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