1991 190E 2.6 Consistent rough idle
 

Yes, I did the search and read it all.

Mine, however, is minor in comparison and has very specific and consistent symptoms:

-- the engines idles roughly EVERY time it is started
-- it only does this for 3-8 seconds, then clears right up without giving it any additional accelerator
-- it does it in ALL temps and conditions, although sometimes is more minor than others
-- sometimes, even if it has been running, it will revert into this if idling at a stop light, etc.
-- it has never failed to start or clear up
-- car has 120k, I bought it 3k ago. Car has had this symptom for several years. Injectors have been replaced about 20k ago. Current injectors have been cleaned.
-- just had my 60k service, which did nothing to fix this problem

Ideas? I'm thinking some sort of vacuum problem but I don't know where to even start on that.

Runs perfectly, otherwise.

Thanks, Phillip

This situation as it's been presented is indeed a bit different than most of the "rough idle" posts that have been listed at this site.

- Short duration @ startup
- Hot or cold
- Reoccurs when warm at stoplight

Take any of these individually, go thru the archives and you can come up the the "most likely" pretty fast, but all 3 together......
This is a tough one.

If it were me, I'd rule out plug wires/dist. cap/rotor, a common cause of rough idle in 103 motors. The short duration you describe cancels that out for me.

I'd suspect fuel injectors were it not for the reoccurrence at stop lights once warm. One would expect an overall rough running condition if that were the case. Wouldn't they?

In other posts here, there's been mention of a vacuum line that runs underneath the intake manifold on 103 motors. It might not hurt to take a look. Also, it might not be a bad idea to examine your motor mounts. They can cause shakiness at idle. I'm not sure if things settel out after 3-8 secs in the event of bad mounts?

Let us know what you discover.

What about carbon deposits on your valves?

What do your spark plugs look like?

Dealer just completed 60k service.