2006 Pontiac Grand Prix 3.8

Hello, the "service engine soon" indicator being on means that the engine's processor has stored data regarding active and / or historical faults from engine performance. This can include areas such as the throttle control. It would be highly beneficial to start by testing to find out what fault data is stored when starting troubleshooting. Anything else is guessing. Performing the needed testing will reveal the source of at least some of the problems that are going on.