My 1992 190E 2.3 starts easily even in cold weather, and idles nicely at around 1200rpm, however exactly 30 seconds later, the idle suddenly drops down to the "normal" idle speed, around 750rpm, before the engine has really had a chance to warm up at all, which results in some stumbling initially. Once I drive off, all is fine.
Is this considered normal behavior? I would prefer that the higher idle would last more like 1 or 2 minutes. I'm wondering if the single prong water temperature sensor by the water pump is what tells the idle air control valve that it's OK to stop allowing additional airflow, and perhaps prematurely makes the idle drop down to 750rpm, by sending a signal that the water temp has hit 40C degrees or so when it in fact has not yet done so.
I would like to hear from other owners to see if the behavior of their cold starts is similar to mine.
The single pronged sensor should be for the gauge.
I think you need to look for the three pronged sensor. There is prob. two of them one for the fan also but it would be easy to just replace them both.
My baby has the same behavour. Idling is perfect though...I had it checked at the dealership, seems nothing to be worried about.
Only difference is the higher revs when driving off with a cold engine.
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My 93 2.3 starts up just like yours and has done so for 153,000 miles. I can see where it could stall if we drove it immediatly and suddenly stopped,but we warm it up for five minutes or so before my wife takes it to work. We live out in the sticks and don't have to deal with too many stop signs. My wife said the car never stalled for her, but it did for me one time just like you described. Its her car not mine.
Hey guys, some more information - I asked a mechanic at the Mercedes dealer about the 30 second high idle time while cold, and he said it was normal. The car is at the dealer for new tie rods, ball joints and a wheel alignment.
I also observed that my mom's 1998 C230 (W202) does exactly the same thing (and this was on a morning when the outside temp was 20 degrees), after 30 seconds, the idle comes down to normal, so I now believe my car is working as designed.
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