190e 2.6 rough idle
 

my 90' 190e 2.6 idles rough after it is warmed up.It drives perfectly but when I come to a stop itidles fairly rough but it doesnt stall.It has 174000 milesand I just replaced the spark plugs, wires,rotor,cap,fuel filter,fuel pumps and fuses.I dont know if this is related but my aux. fans dont come on at all.
please help
Terry

My first thought would be the 02 sensor. When it happens again, try unplugging the 02 sensor and see if that changes things. Do a search in the archives (02 is too short to search on, so try 'oxygen sensor').

rough idl
 

I am having a very similar problem with my 87 300e. Whenever the car is warmed up and at a stoplight or sign, it dives way down. Once it actually died on me. The problem is coupled with a problem in acceleration when the car has just started. If I try to push it any more than a fraction, the whole thing backs off in jolts as if I'm trying to kill it. My first thoughts were a fuel filter or possibly transmission. How would the o2 contribute to this problem?

Because the O2 sensor doesn't do anything until it's hot. At that point, it supplies input to the mixture correction. The fact that you don't have starting problems and the idle is fine when cold tells me that you should check your 02 sensor.

Start by reading this thread:
http://www.peachparts.com/shopforum/showthread.php?threadid=37210

Thanks for the info .I'll see if that helps:)

Is your car actually idleing rough at a stop or is the car shaking giving you the impression the idle is rought?

Your symptons sound like a motor mount, might be time to replace them both.

Another thread on O2 sensors (O2 sensor = lambda sensor).

http://www.peachparts.com/shopforum/showthread.php?threadid=44233&highlight=bosch

Is there any misfiring under acceleration?

After it warmed up I pulled the o2 sensor .It still idled a little rough.I checked the mounts, they are both in good shape.It doesnt misfire when I accelerate and runs great at cruiseing speeds.

Unless the motor mounts have been replaced before (certainly possible), I would be amazed if they are in good shape at that vintage and mileage. In our '91 2.3 with 104k mi I performed the 13mm hex bolt test, and they failed. On visual inspection, nothing seemed amiss. Checking at replacement, the unloaded new mounts were only about 1/2" taller than the old, demounted. The engine used to 'bounce' and knock often when starting and transmit a lot of vibration when cold backing out of the garage. Although smooth and quiet cruising along, noise and vibration would increase a smidge when the suspension would compress traversing bumps and dips.

All those conditions disappeared after replacing the two mounts, and the overall low noise and vibration level went down further.

Steve

Bspoke, did you ever get this problem resolved? I am having the exact same problem on my '87 190e 2.6 (190k mi). Any advice would be appreciated! Thanks.