I have spent numerous hours reading many postings here related to rough idle
and it seems I am in for the big ticket fuel distributor. Please give me
your opinion before I replace it.
The car is a 1989 420 SEL (W126) , 221K KM. I have a rough idle, both warm
and cold, sometimes. It seems one, possibly 2, cylinders are missing,
sometimes. It will idle for 20 secs. perfectly and then it will start to
miss-fire, and the engine rocks, missing for 30 secs, and then run perfectly
again, the cycles are not consistent, sometime 45/15 sec. and other periods.
At non-idle the car does not seem to miss fire.
It has been scope tested, there seems to be no electrical problems. The
dist. cap was opened, the cap was clean, no arcing or deposits. Pulled wire
to cyl. #8, tip was loose, and was replaced. Replaced the injectors and
holders, flushed the injectors before installation. Gas line from the tank
has been replaced, gas filter has been replaced, filter at the fuel
distributor has been replaced, Plugs have only 4k KM, and are the Bosch
copper, W8DC. O2 sensor replaced 2K KM ago. A compression test showed all
cylinders 180 PSI, except #8, which was 140 PSI. Performed vacuum and air
leak test, no leaks detected. Both cams replaced, all rockers replaced.
Chain replaced 4K KM ago. Checked both cam timing marks, on the shaft
compared to the line on the side of the engine, both left and right sides
lined-up, the timing is 0 degrees.
While idling hot, opened cylinder #8 fuel injector line at the fuel
distributor, no change in engine performance. Took the line off the
distributor and no fuel bubbling out. Tried the same thing for cylinder #4
injector line, engine starting rocking more, a noticable difference. So it
seems cyl. #8 is not getting fuel at idle. Loosened #1 cyl. injector line
and the fuel looked dark but then cleared-up, but did affect engine
performance too. I am trying a bottle or two fuel system cleaner.
Does the fuel distributor need to be changed? What should I check or do