I have a 1995 C180 Classic that had recently developed an oscillating idle speed. It used to idle at 750 RPM but now it oscillates between 750 and 2500...just going up and down the revs. It has new plugs and an air filter. I can see no air leaks. At cold the oscillation does not occur but it begins when the egine is at normal operating temperature. Could it be the idle speed actuator? I would be very grateful for any advice.
Thanks,
John

At the risk of sounding like a complete fool, what is a c180? And what injection system does it run?


Joe

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Project Smoker, '87 603 powered wagon
Hauler, 96 CTD can you say torque?
Toy 73 Cougar xr7 convertible
Acme Automotive Inc.
Raleigh NC
919-881-0364

You must be from Europe, as there is no C180 sold in the U.S.

My 300E (3.2) had a similiar, crazy oscilating idle, and the mechanic speculated that it was one of the following:

1. a vacuum leak
2. mass airflow sensor
3. throttle actuator

After replacing the mass airflow sensor and then the throttle actuator, it was discovered that the real problem was the seal at the intake manifold. Replacing the intake manifold gasket solved the problem.

I was left with a $250 mass airflow sensor and a $1,000 throttle actuator that I didnt' need.

Which is why I now have a new mechanic.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

The guys are right, it is most likely a vacuum leak.

However, on my 94 E200 with the same basic engine as you (M111) I had the same fault. I finally traced it down to the water temperature sensor (my car has 2 sensors, 1 for the gauge and 1 for the injection electronics. It was the injection one). I had a poor connection here and could make the revs rise and fall by wiggling the wires attaching to the sensor. Sadly, I wiggled mine once too often and the sensor broke.
Once I fitted the new unit, 100% OK.
Good luck

Barry
E200 Wagon 1994 110k miles.

Thanks for your advice. I live in England and the C180 is a 1.8 litre Mercedes saloon. Apparently these are not available in the States...probably because they are at the lower end of the model range.
Returning to the problem, I took the car in for a diagnostic at the local dealer which indicated a faulty actuator. At great expense and because of time pressure I am also having to have the car repaired by the dealer. This is against my normal practice and makes me appreciate my other car, a 1984 VW, which is not equipped with sophisticated electronic controls and as such has been amenable to my repair over 215k miles.
Once again thanks for you replies.
John

The new actuator appears to have solved the problem.

I've got exactly the same problem on my '95 E220.

Just got mine a month ago & still trying to find out the cause.

I just checked the electrical connectors/plugs and found that one of the plugs on the coolant temperarture sensor was a bit corroded & cleaned it. I drove it for awhile and did not show up. I'll find out tomorrow if that was it. I doubt but let's see. I'll let you know.

I also checked the vacuum hoses for leaks and they all seem to be OK. Idle changes a bit when I pull one out one at a time and goes back to normal when plugged back.

In case it shows up again, where is the actuator on the M111?

John, how much was the actuator anyway? I suppose this can be DIY thing?

Anymore advice on what's the culprit?

Hi,
The idle speed control actuator is attached to the throttle body which is on the inlet manifold. In the UK the cost was approximately £350 but I also had to have it fitted by the dealer because it needed to be electronically set. The actual fitting seems very easy but the need for it to be set !??
The fault could also be intermittent but was more prominent when the car was at operating temoperature. The diagnostic at the dealer clearly indicated the actuator to be at fault in my case and since this was changed the problem has gone. The dealer said that the actuators are prone to go at aprox. 100k miles.
Hope this helps.
John

Since I have the same engine as you, I can tell you that Fastlane sells the throttle actuator for $961 U.S. dollars.

The dealers charge several hundred dollars more.

Do the math at the current exchange rate, and I'll bet it'd be cheaper buying off of this site and having Phil FedEx it to you.

Good luck.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

oh well guys, my idling problems are still there.

actually it's not the same problem as I mentioned earlier. I thought it was a typo error with that 2500 rpm. Mine actually goes down to 450-500 rpm as oppose to going up.

I noticed that it only happens when the car SUDDENLY stops from a relatively fast acceleration. Put it this way, if I accelerate and gained some speed then suddenly stop the low idling shows up. But when I accelerate then decelerate slowly the idling will be normal.

From what I've been gathering, this must be a mass airflow sensor problem. It senses the mass of air IN when the car accelerates but does not react when the car suddenly stops. The MAS thinks that the car is still accelerating or still in motion thus limiting or increasing the air flow (whatever the case may be) and causing the rough idle when the car is actually stationary.

Does that make sense???

Pls. help as this is driving me crazy......obviously.

Dennis

I can't tell you if it's the mass airflow sensor or not, but I replaced mine, and Fastlane sells them for about $240 or so. Much cheaper than the dealer.

I'm telling you, you should check with Phil at Fastlane before you order any parts from the dealer.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".

so rather than start a new thread here's the update- or is it updown- of my stalling problem. got the vehicle back from the dealer who changed the head gasket within two days of the 90-day warranty- so guess I am on my own now. Car ran beautifully this morning- cooler temperature, less humidity. I really though the car was fixed- the brakes even felt 'sturdier'.

About 5 pm temperature 94 outside, start vehicle, circle workplace parking lot, go over speed bumps stop and stop sign- stall.stall-trestarted and sorta thumped into gear- but ths time it went in gear, an improvement from the total lock up. I thought, I was not driving this vehicle correctly- I am not used to an automatic, so I drove 'harder' 40mph with dead and firm stops- okay- out on highway no problem, get to Trader Joe's, buy food. Attempt to pull out of parking space (in reverse) whoa....idle revs, drops, revs, drops, stall.

Drive off highway- stalled three more times- inconsistently, one time just driving along about 35mph and bam. Get to within a mile of home, the vehicle is perfect, purring along, cannot reproduce any stall, hard shift, etc.

Looked under the hood one thing noted a plastic cover that holds down wires going to spark plugs was loose- and on a fresh start when put the car in reverse, that whole part of the engine seems to lift up (which might have loosened the cover or cover lost alignment in heat)- again inconsistently.

And why does this happen only when I'm driving? Car was driven back from dealer two states, hot humid highway driving then traffic and no problem.

Anyway tomorrow hope to get an appointment with local mechanic but sure would appreciate feedback from tech folk here. I also remember reading a post somewhere about a transfer case problem- I wonder if that fits here since the problems seem to occur when the car is driven at lower speeds rather than high speed 55+ then stopping. Though now I am leary about driving over 40 in case it stalls on a turn when I take foot of accelerator.

Thanks for any input.

yes, guys the problem is now solved.

how????

the simplest repair I've ever done.

An MB mechanic friend from the Philippines just told me to clean the throttle valve (the round thing that flaps to let the air in). I removed the air in-take tube and had a look inside and true enough the outer part had accumulated some carbon/dust deposits. Sprayed it with a carburator cleaner, wiped it out and voommmm.

I've been driving it for 2 days now and that idling problem hasn't showed up again and in the past a day won't pass that idling will be go down to 450-500 rpm.

.....just so smooth.

Got car back from a dealership service- 500+ dollars for MAS. I remember posts about MAS but can someone explain what that is (one more time, please). I had hoped it was one of those throttle cleanups only- but I was ready for the most expensive item to be the cause- well the good news is so far vehicle has not stalled and the outside temperature was over 90 degrees. So if this fixes the problem well I'm all smiles...