1986 560 sel rough idle - PeachParts Mercedes-Benz Forum

gwood · #1 08-02-2007, 10:26 PM

I took it to mb dealer replaced distributor cap and plugs 565.00.I got 30 minutes away rough idle started again.Reluctant to take it back can't aford parts replacement diagnosis.Its an intermittent problem sometimes it idles smooth as silk other times it shakes all over the place. Any suggestions would be greatly appreciated.

yal · #2 08-02-2007, 10:41 PM

Can you describe the rough idle? Is it a miss or a chassis vibration? Does it happen in N or P?

gwood · #3 08-02-2007, 10:45 PM

Its a miss,Happens in park or drive

donbryce · #4 08-03-2007, 12:26 PM

Very likely a vacuum hose leak. Remove the air cleaner and check every hose and connection you can see. A leak will also show up if you take your propane torch (for soldering plumbing) and open the valve, wave the tip around near all injectors and hoses, listen for a change in engine speed....and no, it won't ignite even if you hold it next to the hottest part of the exhaust...but someone will probably flame-in here with a warning..
Another possible is oil or something fouling up a sparkplug. Remove and check all of them...could be that the problem has had enough time to re-foul one of them (in my case, I have a leaking valve stem seal in 1 cylinder, change that plug and it will eventually foul again and cause a miss).

gwood · #5 08-03-2007, 03:45 PM

Just had the spark plugs changed.I will check for vacuum leaks.Would a vacum leak come and go.

Thanks for the reply.I'm a first time Mercedes owner and this forum has been an awesome source of info.

Andy_M · #6 08-06-2007, 02:31 PM

I don't know if this car is new to you or not, but my 90 300E had this problem when I first bought it. A bottle of injector cleaner and two full tanks of good quality 92 octane fuel got rid of it.

Mine was going into a rough idle about once per day. Sometimes at a light, sometimes when we stopped and let it idle, sometimes when we stopped and turned it off it would do it when we restarted it. In all cases, getting in the throttle once or twice seemed to clear it and then it would be fine until the next day. Actually the PO had told me about this, but figured it was just because his wife only drove the car to and from work, which was only about a mile and a half away. Could have been she put some cheap gas in it that caused the problem.

Anyway, if you just recently got the car you might want to try this route before you start pulling your hair out.

gwood · #7 08-06-2007, 09:11 PM

Thanks for the advice I will give that a try when I get home.Can't hurt

jhodg5ck · #8 08-06-2007, 10:22 PM

what plugs did you install? If the dealer used Bosch wires it wouldn't be the first set I've seen come out bad.

FYI, the dealers don't know 126's from a Kia these days. You would be far better served to find an indy who is familiar with these cars.

How many miles on her? Does she use any oil? Where does your economy gauge sit while in drive @ idle?

Did they really charge you 550$ for a cap/rotor/plugs? That's a 45 minute job if you take your time.

Jonathan

gwood · #9 08-06-2007, 10:56 PM

Yes they did . Just replaced rotor,cap and plus no plug wires.She has 95000
miles drove it back from California didn't burn any oil got 19 mpg.The econmy gauge doesn't move when its idling but it if you put your foot into it pegs.

jhodg5ck · #10 08-06-2007, 11:00 PM

10 mpg?!?!?!? good god...that's arguable the worst mileage I've heard of yet.. I'd say you have some major issues there...

I wonder if the mixture is horribly rich, perhaps your fuel dist. or EHA is acting up... Either way I'd say you are in for a good bit more diagnostics..

I would have those wires checked w/ an ohm meter.

Jonathan

gwood · #11 08-06-2007, 11:11 PM

That was 19 mpg sorry fat finger mistake

david s poole · #12 08-07-2007, 11:38 AM

you say that this is intermittent problem and the plug wires have not been replaced.suggest that you do so with BERU wires only.if i read correctly between the lines this only happens when car warmed up?

mrwilliepee · #13 08-07-2007, 09:44 PM

Just registered today, Googled this problem and this site popped up.

Pretty sure I'm having the same issue.

It happened while driving, so I let it sit for the weekend. Started it again on Monday, was not there immediately, but then emerged. Oil levels are fine, spark plugs were changed a couple months ago along with a couple of belts, timing chain tensioner and guides, but i did not change the wires.

Similar to the other post, it is not as apparent when in N, but D R P it's there. When stopped, it does shake, but doesn't stall. It seems as if it is only at lower gear/rpm.

Can anyone point me in a positive direction?

BTW it is a 90 560sel with 130k miles.

t walgamuth · #14 08-07-2007, 10:37 PM

my 84 500SEC would miss at idle upon warm start up....sometimes it was really hard to start. I did all the things you guys have done....nothing would touch it. Did some other things too. Previous owner had it into the dealer numerous times with the same thing...never fixed.

One day I was talking to a fellow who used to work on benzos at the dealer locally, back when the 84s were new. He said...."Oh yeah, they always did that....just press the throttle down half way on every startup and it will be fine".....so I did that and also never would shut it off when I went into the vp for a cup of java....just let it run.

The problem was never solved but the half throttle on startup made it livable.

I drove the car from 80k up to 130K in four years and enjoyed the car very much after learning that.

Tom W