'94 E320 uneven idle in Drive when lukewarm
 

When my '94 E320 is lukewarm and it's in Drive or Revers (or any other gear), it idles funny. You can see the rev-counter going up and down, and you can feel the engine revving a bit up and down. If I put the car in Neutral, the problem goes away.
If the engine is fully warm or cold, there's not a problem.

The previous owner told be about this problem, but he had never come around to fixing it. He had replaced the engine wiring loom, so I know that's not the problem.

What could be causing this funny issue?

I was having a similar problem with my '94 E320 Tourenwagen, along with a nasty stumble under acceleration. The previous time this happened it was mostly resolved by replacing the spark plugs, but it never quite went away and then got steadily worse over 15k miles until I could no longer stand it.

After again replacing the plugs but to no effect, I decided to replace the coil packs and spark plug wires, et voila, problem solved: it purrs like a kitten when at idle, no matter how hot/cold, and pulls like a freight train all the way to redline with nary a stumble or shudder.

I love this car.

Both My gassers need new plugs...the wagen...and the intruder.

There is a grey vacuum hose under the intake, in the back, near by the oil filter. If it gets pulled off, the idle will lope up and down. Check that before digging in further.