Rough idle when shifting into D or R when cold
 

I have a problem I can't solve so far -
1992 190E 2.3.
Car starts right away in any temperature.
Idle is correctly higher (around 1300rpm) for the first 30 seconds after start.
The problem comes when I put the car in gear (D or R). The idle deteriorates dramatically and it feels like the engine is running on 2-3 cylinders and shakes terribly. This only lasts for a few moments, and even though it feels like the engine will stall, it never does.
Once I drive away, the problem is gone and there is no hesitation or stumbling whatsoever.
I'm trying to figure out what is happening when the car is put in gear. It seems like there's a sensor that is not sending the proper signal to the computer and too little fuel is being injected to keep the idle proper in gear while the engine is still 'cold'.
I have replaced the 4-prong temperature sensor and it did not help.
If anyone has any theories, I would appreciate hearing your opinion.

Thanks, Mike

Do you have any interior pics of your 2000 C43? It looks like it has all the options such as xenons with washers, rainsensing windshield wipers and all.
let me know if you want to sell your C43.

As requested, here are some interior pics of my 2000 C43. I work for MBUSA. As you may know, there were only 22 C43 vehicles imported to the USA for model year 2000. It has TouchShift, rain-sensing wipers, TeleAid, and headlight washers.

Mike

Did you manage to solve that?

Best Regards.

No, I have not completely solved it yet. After cleaning my idle air control valve for a second time, I noticed a split in the upper breather hose that attaches to the IAC valve. From handling the hose, it simply cracked. Over time the rubber got extremely brittle and when I replaced the hose with a new one today, the old hose was just shattering as I tried to remove it. The new one is nice an pliable. See the attached photo of the old hose. The hose from the air cleaner to the valve cover is another one that can crack easily if it has been on there for many years. I had to replace that hose on my sister's 1991 190E.

By the way, to remove the IAC valve and install it, the only way to get a grip on it and wiggle the hoses on and off is to temporarily remove the oil filter, so that the right hand can reach underneath it.

The new valve and new breather hose improved the idle somewhat, but it's still not where I want it. My next thought is to run a bottle of Techron through two consecutive tanks of fuel to make sure my injectors are clean. If they are not spraying properly, it might cause the poor idle performance until the engine fully warms up. Havent's used Techron in a few months. I'm running out of ideas...

Mike

We have been investigating and we have some data after replacing 3 tensioner pulleys’s but not the solution.

I have installed some time ago a Brabus pulley with a Contitech rubber belt.

We have see that with new belt tensioner, when you start the car in cold, the first 60 seg the tensioner makes some movements (pulls) to the maximum limit and then it stops, after doing that 10 cold starts the rubber mounts of the tensioner limit wear out and you hear that rattling noise.

Then we think that the problem is that the belt is to long, and we should see if on another M111 when you start in cold the tensioner has some normal movement inside the limits if it have then it’s only the belt that is too long and allow the tensioner go to the limit.

Can anyone can make a test (2 people need and a M111 sportcoupe):

With the engine cold after 12 hours:
Mr. A: Enter the car and release the hood.
Mr. B: Open the hood and with a flashlight illuminate the tensioner pulley of the kompressor belt.
Mr. A: Start the engine.
Mr. B: See if the tensioner pulley is stable.
Mr. A: Press the brake pedal and put reverse, move a little bit the steering to one side.
Mr. B: Check if the tensioner pulley is stable or has some kind of movement.
Mr. A: Put Park and stop the engine.

Best Regards.