Or while the car is COLD and running at idle you car spray carb or brake cleaner around spots where vacuum could leak (sealing surfaces, lines, etc..) and see if the motor changes tone at all. Dont Spray around the alternator either. The brushes have a very small spark that can ignite it.
Must Say this. And ALOT of people DONT. Edited for Safety
99 Grand Prix SE-Blue CAI, 3.03 GR Transmission, U Bend Delete.
time to call the exterminator