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I need some help. On idle the 4th cylinder has quit. No problem on rev, just on idle. The 4th spark plug is black (sometimes totally full of gas) other five are ok. I changed everything, injector, spark plug, wires, etc. Pulled the injectors out, all pushed the same quantity. Changed the intake manifold gasket, injector seals, problem stays... I think it's a vacuum problem, but i don't know where to go next.

With a new intake gasket and injector, you can 99% rule out the intake side. Since the spark plug is black and or wet with fuel, it is not igniting as should. That can be a compression problem caused by many things like a burnt valve, but the most likely cause is this though: bad ignition. You can inspect your distributor cap to make sure but my money is on the cyl #4 ignition lead.

Looks like distibutor. Tested the compression, no problem, so the last chance was the distributor. I changed to another one, and now it's fine. I can't go out to roadtest yet.
Thanks for the tips!

So I changed the distributor. The part number shows it's from an e30 323i. It works fine, but the car loss a lot of power. I know this distributors have different timing curves. If I change the vacuum drums it will solve the problem, or need other modifications?

It's the centrifugal weights and springs that determine the timing curve, you'd need to swap those to return to your original timing settings.

polov8 wrote:It's the centrifugal weights and springs that determine the timing curve, you'd need to swap those to return to your original timing settings.

Thanks a lot! I repaired the old distributor, because the another one was....aaarggh. One spring got away on one of those centrifugal weight, because the little plastic crack and loose. Now it's perfect again.