Car is a 1987 300E automatic. When I first start the car in the morning, if the air temp is over 70 degrees or so, the car idles rough for a couple minutes, and it idles at the same 550 rpm idle speed that it has when the engine is fully warmed up. If the air temp is 60 degrees or cooler when I first start the car, the idle is smooth and it idles at around 800-900 rpm. I assume there is a cold engine start mode on the car that is suppoed to bump the idle up a little and richen the mixture, but on my car it does not seem to come into play unless the ambient temp is fairly cool. Anyone have ideas on what this could be? It is not a big deal, but it it's a relatively cheap/easy fix I want to try it. Thanks Andy

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2005 Mercedes C230k sport sedan, 6 speed
1987 Porsche 924S - 968-engined track car

Coolant temperature sensor is my bet. It's the two-pronged sensor near the very back of the cylinder head on the driver's side (assuming LHD). It has two seperate wires on it. One wire goes to the fuel ECU, the other to the ignition module. Fuel is much more sensitive. Both terminals should have some resistance to ground. If one side is open to ground, try switching wires as a temporary fix. About $48 from fastlane.

JFYI, the single terminal sensor is for the dashboard gauge and the three pin jobby is for the radiator fans.

After that, search for the thread on adjusting the EHA. Many contributors to fixing exactly this problem. I learned on my 260E, very similar.

Best of luck,

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Norm in NJ
Next oil change at 230,000miles