Hi all,
Trying to cure an intermittent high idle problem on my '82 380sl. I've tried to read all the posts, but haven't been able to cure mine yet. What I experience seems to be related to coolant temperature. My car starts on the first hit, and the idle climbs to the notorious 1500-1800rpm range where it stays until the car hits appx 82deg. C. As the temp. fluctuates slightly up and down, the high idle problem kicks in. This leads me to believe that it is somehow related to a temp. sensor with the coolant. Is there a method to bypass this switch to see if that cures my problem? Ground it out or so forth? Do they make them for lower temps (I'm assuming not) It seems like a couple degrees down from the normal operating temp (like when the thermostat first opens) and the high idle kicks back in... It is interesting to me, though that sometimes the switch seems to "stick open" and I can start the car after it has cooled off for awhile, (if the idle was normal when I killed it) and the idle settles in to about 750rpm immediately after starting. Then, it's like the switch "unhangs" and the idle jumps again until the car gets warm. Am I making any sense? Thanks gurus!!!!

--Jay
'82 380SL with "High Idle Purgatory" (not quite in hell yet!!)

Not sure if this will help (I've never worked on the car you have), but my 95 E420's coolant temp sensor has decreasing resistance as the temperature gets hotter. If you short the contacts (I used a pair of needlenose pliers), the car thinks that the engine is hotter than it really is, and activates the electric cooling fans.

It sounds like your problem could be that the car thinks it's cooler than it really is. Try shorting the contacts and see if it fools the car into thinking it's hot, and reducing the idle to normal, non-startup (normal idle) mode.

Before you do this - someone please confirm that this won't fry something in the engine, and that an '82 temp sensor has the same inverse resistance with temperature that my 95 does.

Troy
1995 E420 89k