Service engine light came on, idol fluctuates up & down, when car is in park the RPM goes up to 1500, then when you shut car off and restart RPMs are normal for a little while then goes back up again.

I wold check the timing on the Camaro. The slightest nudge of the distributor can cause the timing to go off, assuming it uses a distributor. If it uses a timing chain I would check that as well as the teeth on the chain. If distributor, also check the bolt holding it in place as sometimes they rattle loose. I would use a timing light either way. If you are using a distributor that uses a vacuum advance I would make sure that all the vacuum holes are plugged that are not being utilized. I learned this the hard way.