86 300E won't run over idle speed for 30 seconds or so.

[Ron Miller]

My car has lately decided not to run over idle speed until it warms up for a little bit from a cold start. It will start right up, but when you give it some gas, it either does nothing, or will slow down and die, otherwise it will just idle although a little rough. On older cars with the choke unhooked, you used to be able to pump the pedal for some enrichening of the mixture. When I pump the pedal in my 300E, like I said, it acts like it is not hooked up, then after it warms up for 30 secs or so, it will gradually start revving up to 1200 or so and cutting out, the process is repeated gradually with the rpm going up until all the sudden the car runs pretty good, like after about 60 to 90 seconds. i have no hot starting problems, and the car has only once or twice sputtered when hot since I have had it for about 11 months now. I have put on a new fuel pump relay and distributor and rotor, and changed the fuel filter.

If I missed looking things up in the search please forgive me and direct me in the right direction. Thanks.

[Benzmac]

Try the Overvoltage relay. At times they fail and cause problems like this.

[Ron Miller]

Ok, I replaced the overvoltage relay, and the car is better overall, but now to start it will start about 400 rpm, then sput and sputter for 15-30 seconds and then start running pretty well. I may have to start it 2-4 times, and if I give it any gas, it dies. Once it starts running well, it goes good. In the last few months, I changed the fuel pump relay, fuel filter, distributor rotor and cap, and the overvoltage relay. Any ideas? Thanks, as I am over 200 miles from a dealer and I don't know anybody around my area that works on Mercedes.

[psfred]

Check the hoses on the idle control valve -- its in front of the fuel distributor under the air cleaner, held on by two bolts. Looks like a small beer can, has a two wire conection. If these hoses are hard and loose, they leak and can cause poor cold idle. This is the cheap fix.

Otherwise, it sounds as if you aren't getting the proper mixure cold -- check the coolant temp sensor to see if it as the correct resistance cold. I don't know where that is -- on the head somewhere, I think it has three wires on it. If it is bad, it will give you "closed loop" running mode when the oxygen sensor isn't hot enough to work. Once the oxygen sensor heats up, it will run fine. 30-90 sec would fit this senario.

Peter