I've reviewed the archives and can't seem to find an answer...Any advice will be appreciated !

92 400E 105K...just serviced...
pre service - rough cold idle and hesitation upon acceleration...If accel is moderate to hard, will experience a "backfire" sound up through the throttle intake.."a thud" Also experiencing significant sulfur odors....this odor is more frequent than ever notice prior.

post service - same thing !..no improvement...
The 15K service did not call for replacing rotors and dist caps. I checked mine and found significant oxidation. Removed, Cleaned and replaced.."try that before I replace them with new"...Idle seems to have improved but hesitation is still there.

What could this be?
Need new Dist caps and rotors?
02 sensor?
Something more exciting?

Again, thanks for the input ..
Jeff

__________________
Jeff
'87 300E
'92 400E
'06 ML350