Pontiac Repair: 2003 Montana wont idle down, gas gauge, intermittent problem

Question
DTC P1635, P1639  autoparts guys test says circuit 1 reference out of range, replaced TPS MAP MASS IAC. Intermittent problem happening more often. Idle will hold at 1400-1600rpm in drive and fluctuates 200rpm, when stopping idle will drop with speed to 1100rpm. If I put into neutral while driving 35-50mph engine will rev up to 3000rpm and stay there until braking, rpm seems to drop along with speed,  when stopped in neutral idle fluctuates 900-1200rpm. Also gas gauge will rise to full and sometimes will slowly fluctuate along with tach reading. The inside courtesy lights will flash on while driving (doesnt seem related) have cleaned all the side door contacts HELP

Answer
Hi Wayne:

well you could have a bad sensor one of the ones you mentioned or a wire harness issue or a bad computer and of these are pssable. With out the use of a scan tool to see the engine data stream it's impossable to try to fix. you need to see what the refrence datya and signal data voltage is doing on those sensors.. The root cause of the problme here is affecting the TPS sesnor in all likleyness. you can try to unplug each of the sesnor 1 at a time and start the van and see if the idle drops. keep the TPS hooked up and see what happens. if it idles down when one of thme are disconnected you may have found it.. if not it could be either a bad TPS or computer or wire harness. On that van the wire harness would have issues by the radiator bracket on the drivers side of the van and see is the harness it rubbed on the bracket... Good luck :)