rough idle '96 960

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.