Pontiac Repair: 92 Bonneville

Question
car idle's real high for about ten minute's . then when i hit the gas it goes down. then shortly after it reave's back up continueosly, back an forth. It's a 92'  bonneville SE 3800. I can't hear any vacuum leak's but the car is old? I'm not any expert but if fix thing's and i'm doing this for my grandma and i think it's something to do with the intake manifold vacuum. because it's never been changed?Please help me not look bad!

Answer
Hi James.
well with out a true scan tool there is just a few things you can do. It's either a vacuum leak a stuck IAC motor. you can use a can of carb cleaner and spray around the intake manifold and vacuum lines with the engine running is the idle picks up or sputters you found the leak. if not and it just has a high idle it could be a stuck IAC or an input to the engine computer that is out of whack like a Throttle position sensor. with out seeing it's it's just a guess. good luck :-)