560 SEL rough idlge at start... Only lasts a few seconds
 

1989 560 SEL 120,000 miles: I got a new symptom just recently. The car runs rough for just about two seconds after start. Then it smooths out completely. Does not matter if its a cold or a warm start.

Any ideas?

Might be a faulty fuel check valve, allowing pressure to bleed off after shutdown.

Jim

I know it's not the accumulator. I've had that go bad before. When that went, the car would start great cold, but a warm start took several cranks. Fixed when I replaced it a few years back.

I'll look into the fuel check valve.

Thanks!

i'm working on this myself with a 78 280CE. i believe they share very similar fuel delivery systems.

first, i'd check for vacuum leaks in and around the distributor. don't know if they are similar but mine was leaking, took care of some of the problem.

also check the fuel hoses under the hood and under the car, i found a couple leaky/weepy ones that had to be replaced.

you could also have leaking injectors or a leaking cold start injector/valve. they keep leaking and you have a partially flooded start. or, the thermo time switch could be dead or have a short causing the cold start injector to not work correctly.

do these cars have an air slide valve? what about a warm up regulator, do they have those? these two bosch pieces get wonky over time.

maybe i'm not much help at all...

success in cleaning reassemble pressure regulating valve
 

greets and thanks to everyone, I've gotten so much out of this forum over the years.

'90 560 ~195k (broken odo gear at 192)- over the course of a couple days (cold weather) started rough, then when warm would run fine. I thought fuel, so changed the filter, even though it only had 20k on it. no joy. day by day, worse and worse. I should also add that ever since I've owned it at 160k it surges; oil pressure running up and down slowly. maybe vacuum leak. squirted, found a couple, tightened down the throttle body a bit, still surges. runs, so deal with it later. hood up, neighbor says pressure regulating valve. ok. I live near the junkyards of la, so went to pull one, every 420/560 has the throttle bodies removed already. ok. this am take off a couple fuel lines to pull the prv, (edit: you don't need to do this, it will come off without removing fuel lines) and in what I've found to be typical benz design, the pressure regulating valve has what appears to be a cleanout on it. disassemble, don't lose any parts and count how many revolutions to remove little hex nipple thing, blow with my mouth, exercise the spring in there, blow out with some mas spray, reassemble and joy. starts right up, surging is gone! now it's warm, drives fine, I'll post back if it doesn't start cold tomorrow am. thanks again to everyone.
edit: good news/bad news: when driving wife to work this am, got the goahead to get the focus st. very exciting. now have to wait. boo.

tony

edit: ok so on first driving, ran great, but burned a lot of gas, smoke coming out of the tailpipe. readjusted; or; ended up unscrewing nipple about 4 turns. wouldn't start, screwed in two, too rich, unscrewed 1.5, low idle, screw in 1/2 - idles good and now gets good mileage. lambda seeking at idle, but once warm surging is gone. now the smoke that comes out after a stop light I'm sure is the valve seals, but I've got 6 more months until new car so it can wait. this will be the first car I'll do the valves on. very excited. and again, thanks to everyone.

420 sel surging 560 sel w126 gasoline won't start fuel issue starved