2000 Buick Regal idles rough, 3rd cylinder misfires

I have taken the car to the buick dealership. They replaced the spark plugs and plug wires, no help. Wanted to keep replacing parts until solution appeared, said no.
Went to independent reair guy, he said it was the intake manifold, manifold was replaced, still same misfire at idle. Once the car accelerates it runs like a charm. Just misfires at idle.
Compression is OK, Coils are OK, Wires OK, Plugs NEw, Intake manifold NEw.
HELP!!!
thanks
Jim

I would suspect a bad fuel injector. Whatever it is causing the misfire is specific to cylinder # 3 and you've tried everything else. I have a similar problem with my '95 Regal 3.8L. My car misfires on the number 2 cylinder. It appears to only do it at idle at first. Rev up the engine to about 2000 RPM and hold the throttle steady and I bet you too will hear the engine misfire. It is not too noticable during normal driving.

Yes. check injector.

Thanks for the inputs. I did forget to mention that the tech guy changed the injector with no change.
Jim