Pontiac Repair: 1997 Pontiac Bonneville SE 3800 V-6, intake manifold gasket, pontiac bonneville

Question
o.k. when i start my car it starts o.k. but give it 30 seconds, then the rpm's start to race, sometimes up to 3,000 rpm's, if you shut the car off right away, it will not start again, I suppose it gets flooded.  But if you leave it run for at least 5 minutes, shut it off, wait 25 seconds, then start it again, it runs just fine and I have taken it to my mechanic several times for this and he just can't seem to be able to figure it out. Please help me!

Answer
Hi Bobbi:

well it could be a few things, either a vacuum leak some where of the control of the idle control motor is bad either the motor is bad or the engine computers control of the motor is bad. My guess would be a vacuum leak first and foremost. Has any engine work been done to this lately like an upper intake manifold gasket/manifold or a PCV valve been replaced? If so I would start looking there. if there is unmetered air getting into the engine the engine control computer starts adding more fuel to compensate for the vacuum leak. basically a vacuum leak on an injected car is like you pressing on the gas pedal. it can be a lor of other things like a sensor reading bad and giving the engine computer bad info but I doubt it.. Good luck :)