P1508moderate severityPowertrain
Idle Air Control System RPM Too Low
on 1997 Cadillac DeVille 4.6L V8 Northstar · FWD
What this code means
The PCM detected that the engine idle speed is lower than the specified minimum range and the Idle Air Control (IAC) system is not responding to correct it.
Symptoms
- Low idle speed
- Engine stalling at idle
- Rough idle
- Difficulty keeping engine running
- Stalling when coming to a stop
Common causes
- Faulty IAC valve
- Dirty or carbon-clogged IAC valve
- Vacuum leak
- Dirty throttle body
- Electrical issue with IAC circuit
- PCM failure (rare)
Diagnostic steps
- Inspect IAC valve for carbon buildup
- Clean throttle body
- Check for vacuum leaks
- Test IAC valve operation
- Monitor IAC counts with scan tool
- Check wiring to IAC valve
Repair notes
Clean IAC valve and throttle body. If cleaning does not resolve, replace IAC valve. Check for vacuum leaks.
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