Rough Idle
 

HELP!

I have a 1991 Mercedes 420 SEL (8 cyl. engine) 98,000 miles. Normally at idle you cannot tell whether the engine is running, it's SOO smooth. However, recently the idle became slightly rough. The whole car rattles, etc. Engine performance is excellent in acceleration, etc. however. Doesn't "feel" like it's missing or anything.

WHAT I've TRIED DOING SO FAR and NO SUCCESS: replacing the spark plugs (had 30 k miles on them); exterior cleaning of the injectors and replacing the injector seals (o-rings and sleeves are fine); checking for a vacuum leak (can't find any) ------

ANY IDEAS I haven't tried yet??

Would appreciate any help you could offer. THANKS!!!!

Bob Irving
Charlotte, NC

mounts
 

bob the rattle might actually mean it is the motor mount or engine shocks. This is especially true if the engine is not clearly missing just shaking. If it changes when in gear especially reverse almost garanteed to be mounts.
m

Installed new Injectors from eBay @$40 . Car runs like new !
 

Hi ,
I've been using this forum for some time and officially registered today . I had
the same problem with my 190E and 560 SEL and new injectors fixed it . I
searched everywhere for decent priced injectors but shelling out $500 to
$600 was just too much . Luckily I waited and found new injectors for the
560 SEL for $330 ( $10 shipping ) from eBay . Item number 8029690124 .Give
it a try ! I did change the fuel filter before changing the injectors .
Good Luck !

I second Motor mounts.

Rough idle -- Problem solved !!
 

Thanks to all who replied to my post regarding rough idle in my 1991 420 SEL. After the local Benz dealer AND a very competent shop went thru EVERY possible cause (so they said), and still not fixed, I went ahead and replaced -- guess what -- the IGNITION WIRES -- (hello?) they were the originals and were nearly 13 yrs. old! ! ! And the problem was solved. Runs great! Aren't I a genius? (No, the eye of the owner fattens the horse, thank you....)

That is good news