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1992 190e 2.6, 1995 e320 Wagon
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Discussion Starter · #1 · (Edited)
Hi all. My 92 2.6 has been developing a misfire at idle that is getting worse. I think it's a misfire, the motor just kind of chugs every now and then and the rpms drop momentarily, as if one cylinder didn't fire. I replaced the rotor, distributor, plugs (H9DC0) and wires about a year ago and haven't put that much mileage on them since. The idle was a bit stuttery even then and the tune up didn't fix. The air filter is less than two years old. The only thing I haven't replaced is the fuel filter and that's coming soon but I don't suspect this has anything to do with it.

I checked the plugs yesterday and they appear healthy. My compression is 180 - 185PSI across all cylinders. There is 193k miles on the car.

I have visually inspected all of the vacuum hoses under the air box and around the engine bay and didn't see any unplugged or anything.

More symptoms: when I gas it sometimes there is a whine from the front drivers side of the engine compartment, NO idea what this could be or if it's related. In the two years I've had the car it's done this on and off. Lately it's doing it.

For the past half a year or more "warm" starts I get a really rough idle, but only warm. Hot or cold is basically ok. So if I have just driven the car it starts fine. If I drove the car the day before, it starts fine. If I drove the car a few hours ago and had it in the garage where it's not cold .. rough idle on start, stutters.

Symptoms have progressively gotten worse and now cold starts have gotten rough. They were never a problem before but now it hesitates on idle until it's warmed up. Once warmed up I get the misfire at idle that I described.

I changed the OVP the other night for the hell of it, no change. I also replaced the voltage regulator, preventative maintenance I guess.

The throttle plate is clean, just did that the other night and have always pretty well kept it clean whenever removing the airbox.
IF some crud fell down there though, what could happen?

I also kind of suspect the ICV or the cold start valve. I have VERY poor gas mileage. If my cold start valve was stuck open, would I get the symptoms I'm experiencing?
How does one clean the ICV and should I try that?

Any other troubleshooting steps I should take?
My plugs look ok but the exhaust smells rich and my economy is terrible.

Thanks
 

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1992 2.3 190E
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1,548 Posts
Hey SMP

Well, a miss can be very annoying and hard to find. You can either test stuff or throw $parts$ at it. :) You have been thowing $$$ at her but have not found the issue yet. Though with your mileage, most would have to be done anyway sooner or later so it's all good.

Have you downloaded the manual yet? For example, I don't think a fuel filter will help this issue and rather than just installing a new one you could do a volume check. Same for the Cold Start Valve or even injector spray patterns. I agree none are really easy to do but...

OK, issue at hand. You have taken care of the obvious culprits, plugs, wires and stuff and you feel the miss is only at idle.

Clean Air throttle plate , good for you. This is my favorite thing to go after for a start on key rather than a 2- 3 sec crank and a nice smooth idle. Maybe once a year or just for fun.

But, how are we cleaning it? Spraying Carb Cleaner in there is a no no for Mercedes Mechanics, I read that some where. :) I use a clean rag and spray carb cleaner on the rag and wipe and wipe. Depress and do your best to clean around especially near the top. The spec on the gap is only .002 so if the area is dirty,, well you already know this. Spraying Carb cleaner and junk can find it's way into the ICV .

If it's not plugs/wires/ cap and such the number one answer is a Vac leak. Or maybe a burnt valve but you have excellent compression. The ICV will take care of and compensate for small Vac leaks as they occur up to a point.

I assume the ICV is working OK. High idle on start and 25 seconds later go down to 750 ish? Then there's the hose(s) going to and from the ICV. The one under a tough to get it. When I did my head job the hose's ( large and multi sections from the valve cover side ) were brittle and had to be replaced.

Cleaning the ICV. The experts have spoken, no carb cleaner inside. If you think it is sticking and you can test it by viewing when the Key is turned on. THEY say a few drops of Kerosine is best. I think I used some lamp oil which is Kerosine as that is what I had.

We have a ton of other stuff running on Vac. How's the 1st to 2nd gear shift especially when cold? A hard shift is a good sign of a vac leak. There's door locks, a mess of hoses running the doors for the climate control.

For looking around the engine bay for leaks, spraying Carb Cleaner works as the engine will stumble when you find one. Around injectors, intake manifold. There's more vac lines under the air cleaner near the head side.

One thing puzzling me is the poor economy and the rich smell. Maybe more than one issue. A vac leak should be a lean condition at least at idle.

How dose she go at WOT? That's a whole nuttthhhhher issue. :) Checked for a leaking EHA valve?

Here is a vac miss link that is full of old school methods to find it. I found it to be quite good though much of it you have already eliminated.
Diagnosing Engine Miss

Maybe it will be helpful.

Regards
Dan
 

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1992 190e 2.6, 1995 e320 Wagon
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549 Posts
Discussion Starter · #3 · (Edited)
Thanks a lot for the reply. The car has mostly behaved the same way regarding the fuel economy for the two years I've owned it. I did the duty cycle thing and had to adjust and now I can't remember if I was running lean or rich. I think I was running lean before, but not much. I should test again and see if anything has changed.

That link is great. It's worth the read to me just for this:
Now spin the engine with the starter and listen carefully. An engine in good condition (equal compression across all cylinders) will sound like this:

rrrrRRRrrrrRRRrrrrRRRrrrrRRRrrrrRRRrrrrRRRrrrrRRRrrrrRRR...

An engine with low compression on one or more cylinders will sound like this:

rrrrRRRrrrrRRRrrrrrrrrrRRrrrrrrrrRrrrrRRRrrrrRRRrrrrRRR

The drag on the starter will be less on cylinders with low compression and the sound produced will be uneven.

Oh yeah, and you asked about WOT performance. I think it's good. Back before I adjusted the duty cycle I would see plumes of smoke in my exhaust at night in people's headlights when I really floored it. Car is quick on the highway for sure once it shifts down it gets going pretty good. No idea what to compare to but it doesn't feel slow.
 

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1990 190e 2.6l Calif. auto 1987 Ford F150 4.9L Calif. man 4OD 4X4 2013 Suzuki C50 Crusier
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285 Posts
You might want to put some good fuel cleaner in the tank to clean the injectors. Maybe they are getting dirty. Could be a simple fix.
 

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1992 2.3 190E
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You might want to put some good fuel cleaner in the tank to clean the injectors. Maybe they are getting dirty. Could be a simple fix.
Certainly you can add some fuel cleaner to the tank, can't hurt and clogged injectors could cause a misfire or rough idle warm. but...

1. First I noticed you adjusted the EHA. I cringe when ever I see this. Why, I feel if you are adjusting it you're just compensating for what ever the real issue is.
a) please watch this vid and check for a leaking EHA. "I" believe as the EHA start leaking, failure is a lean condition. At least that is how it Felt on mine when I discovered it. I never never adjusted the Duty Cycle at the Tower. It finally got too annoying and I bit the bullet and paid Bosch their stupid price for a new one.
https://www.youtube.com/watch?v=X1uVnextzeQ

2. The poor mileage, mmm maybe the richer adjustment but I would check to see if the cold start valve is staying on as well. That would be a Rich condition and could also cause a miss.

I have a Bently Manual for my sons 86 BMW, wonderful book. I wish they had one for W201's. But, I do use it for ideas on trouble shooting as the BMW is similar and hey, it's a fuel injector motor. Why bring this up, I am trouble shooting a hunting idle.

One test for a rich idle: Blip the throttle, upon release of the peddle if the idle drops below normal idle then comes right back up to normal, this a Rich Condition ( I would assume here your ICV is working correctly..

I guess this works as a simple test of the cold start valve. Warmed up, just pull the connector and pay attention to the idle.

2. Get in the online manual for your car and go through the Temp. Sensor Ohms test per the graph. It sounds like once warm the ECU is still being told the motor is cold or not fully up to 80C. For you year, you SHOULD have a 4 pin Temp Sensor. This works in diagonal pairs. You start cold, take an ohm reading for cold and just watch your temp gauge. Interpolate the gauge temp as best you can taking a ohm reading at each interval until fully warm.

Same deal, if it has failed it could tell the ECU the motor is cold and keep the cold start valve open.

You also want to make sure the Closed Throttle switch is working. This sends a signal to tell the ECU the throttle is closed.. :) While you're there, you might as well test for WOT signal too.

Enough for now. :)

EDIT: To clarify the Temp Sensor in Diagonal Pairs. As you are testing ohms you need to check both diagonal pairs as you go. One pair can fail, mine did a couple of years ago.
 

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1984 190E 2.3 engine Automatic, 2002 C240 2.6 Automatic
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240 Posts
If your cold start valve was stuck open, it wouldn't run at idle.

If it starts right up when it's cold... and I mean low 30's cold, the CSV is working, and the thermotime switch is probably OK, too. I had a bad CSV, and the car was a terror to start for a couple of days, until I got it replaced.

Last summer, I replaced all 4 of the fuel injectors with OEM parts. This CURED my car of intermittent misfires. One of the injectors had a blob of buildup hanging off of the spray orifice.

As for your missing at idle, my first rebuilt fuel distributor started doing this after a few weeks of running very nicely. Another replacement cured that.

I've gotten really fast with doing work on the fuel system on our cars. I've learned so much!

:bowdown:I like to credit working on a 1986 Pontiac that had throttle body injection. It was my first fuel injection car, and had lots of issues that I cured. When I sold it, it ran great. :bowdown:
 

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1992 190e 2.6, 1995 e320 Wagon
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549 Posts
Discussion Starter · #7 ·
It was the injectors!
Didn't touch the fuel distributor, EHA or anything else. Car has been running poorly for some time, lots of hesitation at idle and off the get-go. Fine on the highway and running problem was only apparent sitting at idle in gear and off the line.
 

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c180 2004
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Was due to exhaust!

my C180 would shut down cylinder 3 when idle, fine if you kept revs up. Back to normal when ignition turned off and back on. It turned out to be a leaking exhaust! New exhaust, problem solved.
 

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1988 190e, 2.3 8v, ~130k miles
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Was due to exhaust!

my C180 would shut down cylinder 3 when idle, fine if you kept revs up. Back to normal when ignition turned off and back on. It turned out to be a leaking exhaust! New exhaust, problem solved.
I know this is an old thread, but where was the exhaust leak?? Before the o2 sensor, or further back?
 

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1988 190e, 2.3 8v, ~130k miles
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10 Posts
Please let us know what spark plugs you fitted in to your engine ??.
At the moment, the wrong plugs are still fitted. Tomorrow, new injectors and new copper, non resistor plugs, but also... the airflow potentiometer, won't arrive til Friday. If it is giving erratic readings theres no sense in trying to adjust the mixture if I understand correctly?
 

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1988 190e, 2.3 8v, ~130k miles
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Update... New injectors installed, New Bosch (H8DCO) proper plugs. Definitely missing on #3 cylinder. Can remove spark plug wire to that cylinder with no change. Going to do (another) compression check tomorrow.
 

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1989 W124 260E
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4,040 Posts
Have you changed over an HT led from one of the other plugs . and is it still the same ? to prove if the ht lead is good .
 
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