Have a Car Question? Ask a Mechanic Online.
Most likely problem is a leaking gasket between upper and lower intakes.
Here are directions for removing the upper intake:
Vacuum diagram to make sure your lines are run correctly:
Sorry, my labor guide software crashed. I believe its around 3-3.5 hours to replace the upper intake plenum. You would be looking at between $280-350 parts and labor depending upon your local hourly labor rates.