1990 300CE-24 Stumble idle after start-then smooth
 

I have a 1990 300CE-24 200,000km, clean, perfect - except that hot or cold, warm or cold weather, intermittently, car starts immediately upon cranking, then stumbles - sounds as if it will stop (has stalled), runs at slow RPM for 3-6 seconds, then resumes normal slightly quick idle.

If I switch it off & re-start, it will start normally.
Leave it for 10-15 minutes, then stumble idles again per above.

Other symptoms:
intermittent sluggish take off from stop start - hesitates for a second while depressing accelerator - then launches suddenly.
engine stumbles at high revs (4500rpm) while still accelerating at high speed.
I am using high octane premium fuel only. The fuel consumption seems OK, although I've only had the car for a week and don't really know what's normal.

Mechanic has:
1. replaced idle air control valve (tested old one and said it was knackered?)
2. new spark plugs
3. new air filter
4. oil change & new oil filter
5. additive put into oil to free up sticky valves (possible cause?)
6. added injector cleaner & other fuel additive to absorb possible condensation in tank

$1000 later, problem has not gone away, and seems worse.

Any thoughts please?:eek:

RE: 1990 300CE-24 Stumble idle after start-then smooth
 

problem ranges from air flow meter sensor, electrohydraulic actuator and fuel system.

RE: 1990 300CE-24 Stumble idle after start-then smooth
 

Thanks sleepwalker.
What is the electrohydraulic actuator?

Do you think from my description that the problem could be a leaky injector(s), noting that the idle problem is most apparent after the car has been sitting around for a while.
That is what the mechanic is checking into next. Is this an easy test, is there a schroeder valve on the fuel rail that can hook up to a fuel pressure gauge and check for fuel pressure loss after pump has shut down.. or is it not that simple to check for leaky injectors? I would hope that the mercedes "expert" working on my car knows how to do this.

It just seems like alot of trial and error. I was hoping to get it diagnosed and fixed quickly without throwing more parts at the car that it doesnt need.

RE: 1990 300CE-24 Stumble idle after start-then smooth
 

doesn't that car have plug wires? sounds like a wire with high resistance, only fails under load. check for burn marks around the plugs and on the wires.

RE: 1990 300CE-24 Stumble idle after start-then smooth
 

Wires were resistance checked be mechanic & checked out OK, so he tells me.
Injectors checked today and found to be OK.

Any other ideas, anyone had a similar problem?