How old is the coil on your car? I didn't see that mentioned. I was having a terrible time with my car and noticed the performance going south when it was wet mostly, and a new coil fixed pretty much all of it - power returned and everything.

Also, its been mentioned that perhaps your mixture is off, so that might need adjusting too.

When I spoke with a guy whose worked on these cars since their inception, he pointed out that sometimes rough idle is hard to track down because the CIS system isn't electronically controlled and that there were new cars that they weren't ever able to fix.

On a side note, be wary of replacing the fuel distributor - its very expensive to replace and most likely isn't your culprit. Its probably electrical.

edit: I see your already suspecting the coil... another thing I was told by the same mechanic is that if you are going to keep the car and its not a new coil, go put a new one on there. There is no way to test them other than replacement, apparently they can test out fine but can also be the problem.

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87 300E
202k on the clock