It sounds like a small vac. leak and possiblty the purge solenoid on the evap canister is junk. Could also just be a cracked vac. line leading to it as well.

The canister is located in the drivers side wheelwell behind the splash shield. Pull the shield and take a look. The purge solenoid should be on top of the canister IIRC.

If that doesn't help, take a look at this thread.

http://www.grandprixforums.net/code-...rol-48791.html