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DTC P1509 - Idle Control System High Rpm

  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. After performing OBD system check, go to next step.
  2. Start and idle engine. Turn off all accessories. Using scan tool, select MISC TEST, then select IAC SYSTEM. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring ENGINE SPEED display. If ENGINE SPEED display remains within 50 RPM of desired value, for each RPM command, fault is not present. If engine speed is not within 50 RPM of desired value, go to next step.
  3. Disconnect IAC valve. Install IAC Noid-Light (J 37027). Start engine. Command engine speed up to 1500 RPM, down to 500 RPM, then back to 1500 RPM while monitoring noid-light. If noid-light cycles Red and Green (never off), go to step 5). If noid-light does not cycle, go to next step.
  4. Check all IAC circuits for open, short to ground or short to voltage. Repair as necessary. If circuits are okay, go to step 8).
  5. Check throttle body for objects blocking IAC passage or throttle bore, excessive deposits in IAC passage, pintle, throttle bore or throttle plate. Check for restriction or vacuum leaks in air intake system. Check adjustment screw for tampering. Repair as necessary. If no problems are found, go to next step.
  6. Check for poor terminal contact at IAC harness connector. Repair as necessary. If terminal contacts are okay, go to next step.
  7. Replace IAC valve. Retest system.
  8. Check IAC terminal contacts at PCM harness connector C1. Repair as necessary. If terminal contacts are okay, go to next step.
  9. Replace PCM. Retest system.
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