New puzzle on a 560 SEL - PeachParts Mercedes-Benz Forum

hbofinger · #1 06-20-2002, 02:19 PM

OK. I've posted here before on a rough idle, and the main symptom has been resolved (thanks to all that posted, especially Maurice!).

However, this did not resolve another, now independent issue I had.

When the car is cold, I start it, go into gear, and off I go. No problems starting.

When the car is all the way warmed up, I start it, and it has no problems on the start. Engine is as smooth as silk, RPMs are correct.

Then I go into drive, and sometimes (and only sometimes) the car hesitates to the point I think it will not go on. This only lasts a couple of seconds, and then car behaves as if nothing has happened. Smooth as a whistle, all the power in the world. It only happens once, and only right after I started the car.

The ONLY other symptom I have, and I don't know if it is related, is that the engine idles high and rough in park, but only when warm, and only in Park or N. In gear, everything is perfect.

Could it be a bad switch at the transmission? The hesitation can't be a leakdown, because the startup is perfect. If it were a fuel pump check valve, it would also happen when cold (never has). Or something in the transmission itself?

Injectors, accumulator, OVP, gas filters, secondary ignition are all new, OEM. 1989 model, 98k miles.

420 · #2 07-22-2002, 10:37 AM

Henry, I have an almost identical problem with my 89 420SEL
It stumbles/hesitates for a second only after start-up, only with a warm engine, and only upon initial acceleration after start-up. My idle was high with a warm engine like yours but I replaced the idle air control valve which corrected that problem.

Were you ever able to diagnose your problem?
Anyone else have any ideas?

I’m going to run some Chevron techron fuel system cleaner through and change the fuel filter but I don’t know where to go from there.

Thanks,

hbofinger · #3 07-22-2002, 12:08 PM

No results yet on what is causing this one. However, since overall she is now as smooth as glass, I am less concerned. Someday I'll figure out the riddle...

#4 07-22-2002, 03:33 PM

Henry - had the same thing on mine - once only. I had driven it about an hour and shut it off. Went to start it about 3 minutes later and when I put it in gear it seemed like it wasn't getting gas - push the gas pedal down and no increase in revs - after about 3-4 seconds it started to have pick up and no problem. I noticed though that that day was 95-98 degrees F outside. I talked to my Mercedes mechanic friend who said don't worry about it - nothing wrong - just a little vapor lock - it can happen from time to time. So -if it did it for you when it was real hot out - could be vapor lock.

hbofinger · #5 07-22-2002, 04:47 PM

Maurice - I think that may be it. Here in D.C. it gets hot. I'll have to see if it's temperature related. It only happens ONCE, ater you start the car and go onto "D". I also noticed it never hapening while going into "R", but it does happen when going through "R" to "D", i.e. I pull out of a parking lot backwards, then go into "D", and oops, she's on strike. And once you are past this hesitation, you are ok. Very strange...