1984 500 sel. bought it not running. needed a fuel pump. fixed that issue. now runs great at 4k rpm, but stalls at idle and stumble and coughs while trying to hold rpms loer than about 4k. stomp on it and it spins right up. but try to slowly add throttle and it coughs and stumbles. when i checked the plugs, they where covered in soot. car was and maybe still is running very rich. replaced the o2 sensor just in case, cleaned the plugs, checked the wires, cap and rotor and all seems to be in order. any suggestions where to look next would be GREATLY appreciated.

 

Lots of people seem to be having trouble with K jetronic system lately.

posted this URL to somebody a few days ago. http://www.auto-solve.com/mech_inj.htm
It gives a good idea of how system works and therefore where to look next.

System pressures are very important since this is how the whole system is controlled unlike electronic systems which have a fuelling map in software,

Since car runs fine at 4000 revs I believe you could for the time being eliminate the ignition side of things.
i would suspect the cold start and mixture control systems which provide adjustment of fuel mix. Should these NOT be working then it is possible the main mixture may have been set high to get the engine to fire up. this would then basically leave the engine running to rich.

Go thru the URL and then come back with a tighter problem definition.

Stuart

 

thanks!!! il be working on it today