P1509moderate severityPowertrain
Idle Air Control System RPM Too High
on 2001 Cadillac DeVille 4.6L V8 Northstar · FWD
What this code means
The PCM detected that the engine idle speed is higher than the specified maximum range and the IAC system is not responding to correct it.
Symptoms
- High idle speed
- Engine revving at idle
- Difficulty slowing engine
- Revving when coming to a stop
- Erratic idle speed
Common causes
- Faulty IAC valve stuck open
- Vacuum leak
- Dirty throttle body with air bypass
- Faulty IAC valve wiring
- PCM failure (rare)
- Intake manifold gasket leak
Diagnostic steps
- Unplug IAC connector and check if idle normalizes
- Check for vacuum leaks
- Inspect throttle body for air bypass around blade
- Test IAC valve operation with scan tool
- Check intake manifold gaskets
Repair notes
Check for vacuum leaks first. Clean throttle body. Replace IAC valve if stuck open.
Other Powertrain codes on this vehicle
P0001
Fuel Volume Regulator Control Circuit/Open
P0002
Fuel Volume Regulator Control Circuit Range/Performance
P0003
Fuel Volume Regulator Control Circuit Low
P0004
Fuel Volume Regulator Control Circuit High
P0010
Intake Camshaft Position Actuator Circuit/Open Bank 1
P0011
Intake Camshaft Position Timing Over-Advanced Bank 1
P0012
Intake Camshaft Position Timing Over-Retarded Bank 1
P0013
Exhaust Camshaft Position Actuator Circuit/Open Bank 1
P0014
Exhaust Camshaft Position Timing Over-Advanced Bank 1
P0015
Exhaust Camshaft Position Timing Over-Retarded Bank 1