300e stalls when watrm
 

I have a 92 300e with the 103 engine. Always starts right up and idles great cold. But when car is warm it wants to stall at idle. New plugs and wires, but i can't figure out what could be the cause. Is this a potentiometer issue?

the potentiometer should be fine if the cold starting and warm up is OK.
Near stalling is normally resolved by a thorough cleaning of the air intake bore and idle control valve ICV .
This should sort out the problem and also set the basis of further checks if required, vacuum pipe leaks ,ignition, fueling etc.
mak
300se/103

What is the condition of the distributor cap and rotor? Is the coil new(er) or original.

Sometimes a bad cap/rotor will cause issues once the car warms up. If they have not been replaced in recent history, then they need to be.

Thanks for the input, I will try suggestions and report back.

Any random lights popping up on the dash? abs cel?

check these items

do a fuel pressure test, check for internal and external leaks, air flow sensor plate and the coolant temperature sensor.

I fixed a stalling when warm problem with a new coolant temp sensor and fixed some leaks at the fuel pump assembly hoses. The resistantance is measured diagnolly( if you have a 4 pin coolant temp sensor) and the resistance MUST be the same or its junk.

Are you plugs black?

I know this sounds dumb, but check the CPS (crankshaft position sensor). Back of engine on top of the flywheel. My car did the same as yours, I replaced almost everything and found out it was this sensor the went out. Replaced it and it ran like a champ.

if it was the cps should be stalling whether the engine is warm or cold.

Often the resistance of the CPS will change as the heat of the engine warms it up. This happened on my 300E....it was "sorta" in spec cold, but got right on the borderline when warm. I replaced it, no more stalling/hard starts. The wiring was falling apart on it too. Best to replace something so critical to the operation of the engine.

yeah but its far fetched since its main job is tell the ezl what postion the crankshaft is at and how fast the engine is going. Stalling when warm doesnt lead me directly to the CPS since it items such as coolant temp sensor plays a much bigger role in determining the air/fuel ratio based on engine temperature.

:confused: Its not far fetched at all. The signal from the CPS is critical to the computer knowing what speed the engine is moving. If the signal is weak or cuts in and out, it will shut down the fuel pumps thinking the engine stopped, hence, stall. Its quite an important part! If it goes out of spec due to temperature changes....it would stall right away. It happened to my car, so it does indeed happen.

proving my point that it doesnt matter temperature the engine is a bad cps will stall with a cold or warm engine. A osilloscope will rule out the CPS.
none of the TSBs for stalling when warm do not mention the CPS. Stalling when warm is caused by rapid pressure drop results in the formation of vapour bubbles in the system. in my case the coolant temp sensor was sending mixed signals to the ke control unit and ezl causing confusion between the ignition and fuel injection

we should know what component is causing it or it may be slight drift off in the air flow due to accumulation of oil, dust etc at the bottom of the air flow passage ,visible if the air flow plate is removed and throttle held wide open.should be spotlessly clean .
mak
300se

I did not mean to start a small uproar. My car stalled only when warm, it ran fine cold.
Got to go about 15-20 miles the first time, then the expense of all the goodies to make it run - and it did not run one tiny bit better. I was at an end of the cars life when I saw something about it on here. The next time it happened (ran fine for 15-20 minutes this time) I bought a CPS, changed it, and never had another problem with the car, no matter how long I drove it or how far I drove it.

To all those mighty thinkers that say it can't happen, I have proof that it can and does happen.

I didnt say rule out the cps when dealing with a stalling issue but its not one of the first things I am going to check especially when tracking down a stalling when warm problem. If the most common things that cause a stalling when warm problem check out then ill go other places.