butch

The patient is a 93 300e with the M104 motor, with 101K on the clock.

Three months ago started to get a weak idle after the car got to running temperature.

Had a 30K service done to include plugs and associated parts, oil change, air filter, coolant and transmission change, and fuel filter. At the time I also had the valve cover gasket replaced.

Problem has persisted, so additionally the MAS, Oxygen Sensor, Vaccuum system, and Throttle Actuator were checked and found to be fine. My indy, try as he might can't find the source of the poor idle, and as a default has suggested it may be the wiring harness.

However, my wiring harness was replaced by the dealer in 99 when it had 58k on the clock. The OVP and Fuel Pump relay were replaced about a year and half ago when I acquired the car.

So what think ye?

All replies appreciated.

paul9662

I had a similar problem a few weeks ago after a servicing. Turned out to be plug wires. Good luck.

bamberger_1

rough idle can have many, many causes. But a few checks before seeing the dealership are, the igniton cable the previous poster said. Another option could be that the engine sucks additional air somewhere, like the injector seats, the vacuum hosing, the rubber parts of the inlet manifold. To check this you need brake cleaner, take of the airfilter and spray it on those parts (not into the air inlet) when the engine is running. As soon as the idle speed goes up you found the area where additional air gets into the circuit. My guess is the that the injector seats are worn out. The other thing is the cold start valve, if it does not close after warm up and the mixture gets to rich. You can check the valve by pulling it and applay 12V then it opens, as soon as you remove the 12V it should close and not keep dripping gas.

BigKid

The 104 motor doesn't have a cold start injector, thats on the CIS fuel system. The '93 104 motor has the HFM system. Check the fuel pressure regulator for leaks, also check the MOT valve on the drivers fender for a vacuum leak ( with the engine running the valve should pulse, if no pulse pull the hose that returns back to the tank and feel if there is vacuum on the valve nipple. there shouldn't be any unless the valve is pulsing). Another thing to check is the fuel pressure at the pumps. The pressure should be 2-4 bar (28-56 psi). If its higher than 4 bar the no.2 pump is bad, if its lower than 2 no. 1 pump is bad.

AMG_Eric

could be a head gasket. if you have a small leak there u can get rought idle as well as your coolant maybe slowly evaporating.

the other thing it could be is the throttle acctuator.

butch

Thanks for all the info. We're going in to see a noted local Indy tomorrow morning for diagnosis.

AMG_Eric

where do you live?

butch

I'm in Cincy.

Problem found, coil packs in the ignition. Car runs like new again.

thanks for all replies