1991 560SEL - rough running

[Karl's MB560]

This is a 1991 560 SEL w/ 140,000 on the clock. Car has been running great, but all of a sudden,when engine starts - cold - starts promply, runs smooth briefly, then appears to be 'mis-firing'. At normal cruising speed, engine appears to be smooth and rough - intermittently - and, if accelerated, roughness is apparent; sometimes when coming to a stop - in traffic - engine will completely stop, but does re-start, still running with a mis-firing type behavior. Initially, I thought I might have water in the fuel system, but I don't think so anymore. Hasn't been tuned for some time, but monitoring the fuel consumption has shown 18 - 21 mpg highway driving. Any ideas?

[eric242340]

Pull the spark plugs out and take a picture, keep them in order ie 1 2 3 so we know which cylinder they came from, then I may be able to advise you.

[Karl's MB560]

Thank you, Eric, for responding; I will do this; however, as I will be traveling beginning today (01/01/2013) for the next ten days, I will not be able toget this back to you until about 01/13 or so.
Again my thanks.
Karl

[sthomen]

Originally Posted by Karl's MB560

This is a 1991 560 SEL w/ 140,000 on the clock. Car has been running great, but all of a sudden,when engine starts - cold - starts promply, runs smooth briefly, then appears to be 'mis-firing'. At normal cruising speed, engine appears to be smooth and rough - intermittently - and, if accelerated, roughness is apparent; sometimes when coming to a stop - in traffic - engine will completely stop, but does re-start, still running with a mis-firing type behavior. Initially, I thought I might have water in the fuel system, but I don't think so anymore. Hasn't been tuned for some time, but monitoring the fuel consumption has shown 18 - 21 mpg highway driving. Any ideas?

Sounds to me like the EGR..

[Karl's MB560]

Thanks for the 'EGR' reply. Now I must show my ignorance. How would I
pursue 'looking' at this?
Also, Eric has asked that I pull the plugs, photograph them, which I intend on doing when I get back from traveling - this will not be until January 13.
Karl

[sthomen]

Originally Posted by Karl's MB560

Thanks for the 'EGR' reply. Now I must show my ignorance. How would I
pursue 'looking' at this?
Also, Eric has asked that I pull the plugs, photograph them, which I intend on doing when I get back from traveling - this will not be until January 13.
Karl

Not sure on that car, Its going to be on top of intake man, near dist cap, or in front. Lookup part so you know what to look for, when you find it get car hot than tap it a few times. If its stuck it should pop open then

[Karl's MB560]

Thanks for the QUICK REPLY. I will follow your guide, and let you know the result.
Karl