I have a '85 380SL that I have been doing some minor repairs/tune-up on. One problem that I cannot resolve is the car surges at idle and when decelerating the car will stall. The stalling does not happen all the time but intermittently. I have replaced spark plugs & wires, O2 sensor, and adjusted air/mix. Any suggestions as to what is causing the surging and stalling? Are they related?

Take off the air cleaner and spray carb cleaner around the intake manifold, injectors and see if the RPM's increase. You may have an air leak.

I tried the Carb Cleaner suggestion and I did not notice anything different from the surging that I've been experiencing. Not related to using the carb cleaner but part of this same problem, if I rush the engine and then let it idle it will surge continuously for several minutes.

My mechanic had the car running very rich (lot of carbon out the exhaust). After replacing the items mentioned in previous posting, that problem was cured. Could the catalytic converted be plugged from all the soot and be causing this problem.

I spent 18 months hunting down a surge and stall problem like this. I changed plugs, distributor cap, air slide valve, idle speed control, OVP, fuel pump relay and finally found that it was the ignition control module. Look in the driver’s side fender well and see if your control module is loose. Also, see if it really hot, not just warm. Mine would get scalding hot. If you have a problem identifying it, it is a silver box that has a lead to the coil. Mine was loose and so was the one in my friend’s car. His was still good, but mine was bad. Replacement (Partsshop) cleared up the major problems. Look for unstable tachometer readings when it is going nutty because they share a ground. My fuel pump relay also was clicking like mad. Good luck because these are not easily diagnosed.

Steve
’85 500SL Euro

I have a 380sl that stalls or stumbles under heavy accelleration, the tach freaks out when this is happening. ( goes from 3000 rpm, to 1000, and then back to the operational rpm) Is this what you are describing?

this thread is 6 years old , the originator is long gone. but you can post a new thread with your 380 problems for best results .