Pontiac Repair: 99 Pontiac grand am that reads P0300, P0105, engine vacuum, vacuum leak

Question
I have a 99 Pontiac grand am that reads codes P0300, P0105 and P0108. The car starts and runs good, but it stalls, rpms go down, and die during a stop, park, reverse or neutral. We have replaced the TPS, MAP and the fuel filter. We think it can be the IAC valve, but we are not sure because we took it off and turn the car without it and the car didn’t die.  Then we tried the car with two used IAC valves and the car still didn’t function right when we change valves.  We are not sure if we should replace it with a new one or what the problem can be. Please help.

Answer
Hi Martha:

what engine is in this car? 4 or 6 cyliunder?

If it's a 4 cylinder the vacuum hose going to the MAP sensor could have a rip or tear in it and that was a VERY common issue with them an dthey would set those codes and run like you say yours is. The problem is not going to be the IAC valve it more then likley has an issue with the vacuum supply to the MAP sensor or the wiring going to the sensor. If it's a 4 cylinder does the engine have any kind of abnormal nose from the fron of the engine ? it could be possible the timing chain may have jumped if there is noise. the timing being out will cause it to run bad as well and effect the engine vacuum it's self. If this is a 6 cylinder I would check for a vacuum leak again or it would have to be a wire issue going to the MAP. good luck :-}