My 1998 STS runs fine, while at idle for a long time the check engine light comes on, I pulled the codes and got P0300. I does not ever seem to idle ruff.

just some history, I changed the Head Gasket last year. and I replaced the spark plugs and hoses, I did not change the coil packs and think that might be next.

Any Ideas?

Did you change the plug wires? If not, that's what I'd change next (A/C Delco).

i will do that today,

is there a way to test the coil pack? they cost $100 and dont want to spend that unless I have to

You can pull the coils and look for signs of arcing at the plugs or listen to them with a rubber hose for arcing. I think you can test the resistance, but I'm not sure what it should be.