1992 300sd. runs smooth, idles good. valves alittle noisey @ idle. no smoke. other times idle rough almost a skip, and smokes unburnt diesel. have bad wiring harness? will that effect timing or fuel delivery, or bad injector. comes and goes? any help would be appreciated.

Checked compression? Before I did the head replacement on my 300d, mine would do the skipping at idle with unburned diesel out the pipe (along with a good bit of blue oil smoke due to other issues). It wouldn't do the skipping thing, though, if I burned 45 cetane diesel or biodiesel. Of course, my compression was low--120 and 100 on 3 and 4. Yikes.

Timing and fuel delivery are controlled by timing chain. Checked stretch lately?

__________________

1998 E300D, 287k, barely broken in.

Some things to consider:

Valve adjustment
Have injectors inspected/cleaned/Diesel Purge
Rack damper adjustment

You can search for these and find a number of threads...

__________________
marshall

1982 300TD (220,000 mi.)

do these things along with a couple of italian-tune-ups, i find this solves my problem.

__________________
82' 300SD

could it be mechanical and still be intermitten?

Is the rough idle consistent with cold or hot engine temps? Valves, chain, ip timing, I think, would cause constant problems hot and cold. I would suspect filters first, injectors second. Try cracking injector lines at idle and see if idle is affected. If idle is consistently rough when an injector line is loosened, switch that injector with another and see if the problem follows that injector. But you should check the other things mentioned as well and post back.

__________________

1998 E300D, 287k, barely broken in.