rough idle '96 960

Just wondering what would cause a random misfire at idle. Engine is
fine when driving.

No vacuum leaks, wiring harness and coil packs okay, compression fine.

Any suggestions to what else I should look at?

 

You just listed all the things I'd normally check first. How are the
spark plugs? Maybe time to have the fuel injectors cleaned?

 

Water in the tank or bad fuel.

 

Could all six injectors go bad? At the same time?
OBD throws misfire on all six, plus random misfire. Keep in mind that
when driving, engine runs fine. No sputtering, missing, fuel smell,
etc.

 

Well not so much go bad, as just gradually get dirty, it's pretty common
for the whole set to get about the same amount of contamination because
they all pass about the same amount of fuel from the same source.

My first guess would have been vacuum leaks, but you say you've got that
covered. Could also be something with the ignition, but you say the
coils all check out fine. I suppose it could be a bad ignition module,
does a single module drive all the coilpacks on those? Since it's across
all six cylinders, it's almost certainly something that deals with all
of them. How about the fuel pressure regulator? Fuel pump issues? Does
the 960 use a pre-pump in the tank with a main pump under the car, or
just a single main pump? Does the symptom get worse when the tank is low?

The most likely thing still comes back to vacuum leaks. There are
countless places for a leak, have you checked everything? Brake booster,
air intake plumbing, crankcase ventilation, vacuum reservoir for the
HVAC system. Air mass meter is another possibility, know anyone else
with a 960 you could try a swap with?

 

I ran some seafoam thru the gas; I'm assuming that cleaned the
injectors.

Still has a rough idle

Where is the ignition module in this car?

 

That can help a bit, but to do a thorough job and know the results, the
injectors have to be pulled and run through a testing machine and
ultrasonic cleaner.

No idea where the ignition module is on those, I've never worked on a 960.