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2004 AUDI A8
4.2L V8•AWD•AUTOMATIC•gas•BFM
1 active safety recall on this vehicle — view recalls
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Repairs0Labor487Torque2164Fluid10DTC956Battery1Maintenance0Recalls1
P0505moderate severityPowertrain

Idle Air Control System

on 2004 Audi A8 4.2L V8 · AWD

What this code means

Malfunction in the idle air control (IAC) system.

Symptoms

  • Erratic idle speed
  • High idle
  • Low idle
  • Stalling at idle
  • Fluctuating RPM

Common causes

  • Faulty IAC valve
  • Carbon buildup in IAC or throttle body
  • Vacuum leak
  • PCM issue

Diagnostic steps

  1. Clean IAC valve and passages
  2. Clean throttle body
  3. Test IAC valve operation
  4. Check for vacuum leaks
  5. Monitor idle RPM with scan tool

Repair notes

Clean IAC valve and throttle body first. Replace IAC if cleaning fails.

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