Pontiac Repair: erratic idle 3.4l, throttle position sensor, vacuum leak

Question
we have a 93 grand prix 3.4L with an idle problem most mornings surging to 3,000rpms only during winter.idle would return to normal when car warmed up.now rpms do not come down.few years ago had timing belt replaced.problem went away for a short time but returned.i recently replaced upper intake gasket,because i believe that was removed when timing belt was done. idle was fine for about a week.now back to old ways.also early this winter before i changed gasket ilde was normal for a few days??thought it was a vacuum leak now i'm not sure. thanks

Answer
Hi Paul:

you are close it is a vaccum leak more than likely but the lower intake gasket leaking vacuum. It's pretty common. the only other cause could be the a/c pressure sensor in the high side a/c line they have a tendency to short out and when affects the throttle position sensor. The vacuum leak is the most common cause. Good luck :}