i have a 93 sl2 twin-cam sedan. my check engine light comes on while driving and turns off by itself then will come back on shortly. when you start the car and begin driving right about when it would shift into 3rd gear (automatic) the engine bucks like crazy and bangs hard, then it shifts. however, it will only do it after starting ther car, you can come to a stop and start going again and it wont do it, it has to be after a new ignition cycle. i tried replacing the egr valve hoping that the exhaust gases were not recirculating properly and were trying to escape but no luck there. i am stumped and wondered if anyone out there has had the same issue or might know of what to check out, thank you!

 

You may have a loose output shaft nut or the tranny vavlebody may be going bad. Both items to be taken care of by someone that knows about the items and how to fix them. Welcome to the forum.