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2002 CADILLAC DEVILLE
4.6L V8 Northstar•FWD•AUTOMATIC•gas
5 active safety recalls on this vehicle — view recalls
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Repairs0Labor491Torque4250Fluid7DTC1027Battery1Maintenance0Recalls5
P1509moderate severityPowertrain

Idle Air Control System RPM Too High

on 2002 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

  1. Unplug IAC connector and check if idle normalizes
  2. Check for vacuum leaks
  3. Inspect throttle body for air bypass around blade
  4. Test IAC valve operation with scan tool
  5. Check intake manifold gaskets

Repair notes

Check for vacuum leaks first. Clean throttle body. Replace IAC valve if stuck open.

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