I own a 1992 745 that has Regina FI system. The car idles rough only when in gear (worse when a/c is ‘ON’), idles fine when in ‘Park’, so this may not be the same problem you’re having but it may be something to consider. A local Volvo mechanic – knowledgeable and respected, told me that this is a common problem with Regina FI systems. It can be cured by reprogramming an EPROM or something like that. He said it takes care of this problem and also gives about ten or fifteen more horses! I haven’t had it done so I don’t know if it works. The cost is about $130. Hope this helps in some way. I can only imagine how frustrating this must be. At least when you solve the problem the car should run great considering all the things you’ve done. Good Luck!

Michael
Melbourne, Fla

1985 740 460k (original motor)
1988 780 Coupe V6 181k
1989 780 Coupe V6 149k (parts car)
1992 745 195k