Expert: Kevin - 6/15/2009

Question
Check Engine code showed P0505 motor still ran, but idled a bit rough.  Replaced IAC and ran better for about 5 miles.  Then turned off motor and when restarting it motor will not idle, but dies unless giving it gas.  Replaced with another new IAC and same thing.  Put back in original IAC and check engine light came on again and engine idles rough, but runs?

Answer
P0505-IDLE AIR CONTROL MOTOR CIRCUITS
When Monitored and Set Condition:
P0505-IDLE AIR CONTROL MOTOR CIRCUITS
When Monitored: At power-up and battery voltage greater than 11.5 volts.
Set Condition: The PCM senses a short to ground or battery voltage on any of the four
Idle Air Control (IAC) driver circuits for 100 msec while the IAC motor is active.
POSSIBLE CAUSES
PCM (IAC DRIVER #1)
PCM (IAC DRIVER #2)
PCM (IAC DRIVER #3)
PCM (IAC DRIVER #4)
IAC INTERNAL FAILURE
IAC MOTOR DRIVER CIRCUIT SHORT TO VOLTAGE
IAC MOTOR DRIVER CIRCUIT SHORTED TO GROUND
IAC MOTOR DRIVER CIRCUITS OPEN
PCM - IAC 12 VOLT DRIVER OPEN
PCM - IAC GROUND DRIVER OPEN
DTC NOT EQUAL TO FREEZE FRAME DTC
IAC MOTOR WIRING HARNESS INTERMITTENT
IAC MOTOR
IAC #1 DRIVER CIRCUIT SHORTED TO #2, #3, OR #4
IAC #2 DRIVER CIRCUIT SHORTED TO #3 OR #4
IAC #3 DRIVER CIRCUIT SHORTED TO #4
IAC #1 DRIVER CIRCUIT SHORTED TO GROUND
IAC #2 DRIVER CIRCUIT SHORTED TO GROUND
IAC #3 DRIVER CIRCUIT SHORTED TO GROUND
IAC #4 DRIVER CIRCUIT SHORTED TO GROUND
IAC #1 DRIVER CIRCUIT OPEN
IAC #2 DRIVER CIRCUIT OPEN
IAC #3 DRIVER CIRCUIT OPEN
IAC #4 DRIVER CIRCUIT OPEN