I've had this problem for about a month. Car starts right up. Runs smoothly. After two or three minutes, before the engine is up to operating temperature, in park or at a stop sign in drive it starts running rough. I can put it in neutral, rev it up a few times and it idles fine. If I don't rev it up and take off it bucks a little and is then fine. Then until the next day it starts and runs fine all day. No check engine light. 113,000 miles. This weekend I replaced spark plugs, wires, coil packs and the five crankcase vent hoses. No change. I didn't expect any of those to be the issue, but it was past due. As preventive maintenance I had D.J. refurbish my RCM in July. At about the same time I replaced the camshaft and crankshaft sensors. Both were Bosch. I'm thinking one of the O2 sensors. Any ideas or comments

 

What kind of gas are you using? Have you tried an injector cleaner? You can also check fuel pressure at the rail. It should be about 58 psi.

 

I only use Shell Premium. Top tier. If the injectors were dirty, I don't think I would have such a smooth idle and quick acceleration.

 

Did you clean the Throttle Body and MAF when you were doing all the other things ... if not, you might try that

 

Thank you, DeKalb. I'll do that today. I should have done that when I had it off for replacing the crankcase vent hoses.

 

Pretty basic but how old are your air filters?

 

Exhaust Gas Recirculation valve (EGR) will cause rough idle when it is stuck open. For the first three minutes of operation the auxiliary pump is probably running and the car is in closed loop; after three minutes it goes to open loop and the stuck open EGR valve may be your problem.

 

Thank you ZERACER. I changed those this weekend when I had everything apart. The old ones were about a year old. They had some bugs but didn't look too bad.

 

Thank you zip439. Since I'm not getting any fault codes is there a way to check the EGR valve for sticking open? FCP Euro has the genuine Mercedes for $188.99. I don't want to start throwing parts hoping that is the problem.

 

I agree with M60A3Driver Run a bottle of

Chevron Techron Complete Fuel System Cleaner thru your engine.

 

Here is my solution I found with my EVAP valve. I plugged the vacuum line from the intake to the EVAP valve. Which led me down a issue with gas in the charcoal canister. Fuel in Charcoal Canister

Plug it up


This will give you the idea that the problem is upstream of the EVAP valve.

 

The picture above is not the EGR valve .

It is the EVAP solenoid. It too can cause rough idle, but as the OP says his trouble starts after three minutes that leads me to believe the car changing from closed loop to open loop is involved in the problem. The EVAP solenoid will open/close per the PCM after the car is up to operating temperature, has operated for awhile and then goes to idle. The EGR valve should always be closed at idle.

However, plugging the line going to the throttle from the solenoid as you indicate will differentiate between either problem.

 

You're right. I have corrected my description.