This is one problem that my car has had since I've owned it and nothing I've done/changed over the last 3 years has affected it, until now. I had given up on worrying about it. Basically, on any cold start where the car had been sitting for 6+ hours the engine would stumble hard during the first 2-3 seconds of startup and then go right to a steady smooth idle.

I removed the ICV and cleaned it out, although it wasn't too dirty. I also replaced the two rubber hoses that plug into it. The old hoses were very hard and brittle, but didnt see any obvious damage to them. The hose that the CSV plugs into is a real b!tch to r&r. After doing that, cold starts are b-e-a-u-t-i-f-u-l. I can say today was the first time in thousands of starts since I've owned it that it didn't make me cringe!

I should also mention that I also had a rhythmic pulsating idle when the car was warmed. Turned out my old alternator was barely putting out enough voltage at idle. New 120A S-class alternator a few months back fixed that and the idle is very smooth and quiet now. Just another thing that can affect your idle that is not related to typical spark/fuel/vacuum issues.

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1991 300E - 212K and rising fast...