lately i have been having this problem with my 89 shadow. Its a turbo 5spd with the 2.5l. It seems to have this problem anywhere from 5 seconds to 3 minutes after start up and will continue until you shut it off. sometiimes it does it and othertimes it wont, but lately its more frequent. The tach will start jumping all over the place like up and down within 500-1000 rpm of where it was when driving and will cause the engine to misfire. It will do this while idling or driving. It was getting so bad (shuttering) that the alternator would stop charging and would show a code 47, battery below target voltage. I have tried swapping coils, coil wires, checking the plastic rivets in the distributor, cleanin the cap and rotor even unbolting and cleaning all the grounds with sandpaper including the connectors on the alternator. It seemed to help a little doing the grounds yesterday, and it drove fine this afternoon but started to shutter again while driving home from work. so does anyone have an idea to where they can point me next? any help would be appreciated as i do like the car and how fun it is and would like to beat that guys bmw before winter with my $500 car(pretty even race last time).