jlee4171

Hello MB experts. I need help identifying the problem with my car, with only 116k miles, car drives fine once it gets going, no rough idle or stalling issues. Car starts fine with engine cold (like first start in the morning), and car starts fine when engine is relatively hot (like after stop at gas station or a quick meal). Car normal idle is around 800 rpm. The issue is after running the engine and let it sit for about an hour or so, temperature gauge dial drops from 80C to about halfway down to the bottom (like about 60C), that's when it will start and dies immediately. It usually starts on the second try, but one time it took me 4 or 5 tries to get it started. One thing I've noticed at a cold start (like in the morning), the idle remains pretty low at around 800 rpm, I thought the choke(?) would keep it at a higher rpm like above 1000 rpm or so, then drops down to normal running temperature after engine warms up...but not sure since I am not familiar with the Mercedes car choke function...maybe that is normal?? Previously I posted the same question and someone pointed out it may be the Fuel Pressure Regulator, and advised to keep the key in position 2 a little longer before cranking, I've tried numerous times and it didn't seem to help. I am thinking it may be related to something like the idle control or something to do with the choke, any ideas? thanks in advance.

HedonisticFrog

There's no choke on a KE jetronic system for starters. If you think it's fuel pressure related then you should get a fuel pressure tester and see if the fuel pressure is dropping when it's acting up. I just had a somewhat similar issue with my 1987 420SEL where it had difficulty starting, the idle wasn't stable, and it would hesitate under acceleration which turned out to be a bad engine ground. It's a quick easy thing to check, bad grounds will give you weird symptoms.

jlee4171

Thanks HedonisticFrog. So in the morning or when engine is cold, is your idle speed stays at a higher rpm than the normal running rpm, or is it like mine that keeps it at about 800? I don't remember the last time my engine stays at above 1000 rpm during cold start.
If it's fuel pressure related, why is it only acting up when engine cools down, and not an issue when engine is completely cold, or hot?

JohnLane

OP worth checking is ‘false air’ AKA vacuum leaks. A smoke machine is most effective for finding them.

adler

Idle