OBD-II Code · Powertrain
P0506
Idle Air Control — RPM Lower Than Expected
Severity
medium
Worth booking. It costs fuel, emissions or comfort until it is fixed.
Can you drive it
Only if running normally
A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety.
Indicative cost (USD)
$50–$400
Varies by vehicle, diagnosis, parts, and local labor. This is not a repair quote.
Idle speed lower than commanded.
How a shop works this
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed.
Note every code that is set, not just this one.
Codes that appear together usually narrow the cause faster than any one of them read alone.
Read the freeze frame — the conditions the fault was recorded under.
Cold or warm, idle or load, road speed and engine speed. A fault that only appears cold is a different fault from one that only appears under load, even with the same code on the scanner.
Confirm the fault is current rather than history.
Clear the code and see whether it returns under those same conditions. A code that does not come back may have been logged during a repair, a flat battery, or a bad connection that has since been disturbed.
Then work the likely-causes list in the order shown.
That order is what a shop checks first for this code — wiring and connections before the component they run to, because a connector costs nothing to inspect and is a common answer.
If the code comes back after a repair, the underlying fault is still there. That is the point to bring in a scanner with live data and freeze-frame, or a shop that has one.
Common symptoms
- Stalling at idle
- Hard restart after stall
- Check engine light
Likely causes
- Dirty throttle bodyMost common
- Failing IAC
- Vacuum + load issues (AC clutch stuck on)
Read the full diagnostic procedureP0506 sets when the PCM measures actual idle RPM at least 100 RPM below target with the IAC commanded fully open, indicating restricted idle air or e…
P0506 sets when the PCM measures actual idle RPM at least 100 RPM below target with the IAC commanded fully open, indicating restricted idle air or excessive load. This is the most-searched IAC code by a wide margin, and the cause is almost always carbon buildup or a sticking IAC pintle rather than an electrical fault.
Cheapest-first diagnosis
- at warm idle, scan target RPM versus actual RPM and IAC steps, a P0506 vehicle typically shows IAC pegged near max (180+ steps on GM, 60+ percent duty on Ford) while actual RPM lags target by 100 to 300 RPM. Pull the IAC and look for a black varnish ring on the pintle and a sooty deposit in the throttle body bore; clean both with throttle body cleaner and a soft brush.
- Check for a stuck-closed PCV valve, a binding throttle cable, or a dragging A/C compressor that loads the engine at idle.
- Run an idle relearn after cleaning.
- The expensive misdiagnosis is replacing the torque converter or transmission when the actual fix is a $10 PCV valve and 20 minutes of throttle body cleaning.
Vehicle-specific patterns1999 to 2007 GM 4.8L/5.3L/6.0L Vortec engines (Silverado, Tahoe, Suburban) set P0506 from cold-stall vacuum leaks at the upper intake manifold gasket…
- 1999to 2007 GM 4.8L/5.3L/6.0L Vortec engines (Silverado, Tahoe, Suburban) set P0506 from cold-stall vacuum leaks at the upper intake manifold gaskets, GM TSB 06-06-04-037, the plastic manifold warps and the gasket lets in unmetered air at startup.
- 2003to 2010 Chrysler 5.7L Hemi sets P0506 from a cracked PCV hose and a sticking IAC, plus intake manifold runner control issues.
- 2000to 2006 Honda Accord 2.3L sets P0506 from carbon at the IAC and a sticking EGR valve.
- 1998to 2004 Subaru Outback with EJ25 sets P0506 from intake manifold gasket leaks at the runners.
Estimated repair$40 to $650.
Look up another code
P0506 — frequently asked
What does a P0506 code mean?
Idle speed lower than commanded.
What causes a P0506 code?
Common causes: Dirty throttle body; Failing IAC; Vacuum + load issues (AC clutch stuck on).
What are the symptoms of a P0506 code?
Typical symptoms: Stalling at idle; Hard restart after stall; Check engine light.
Is it safe to drive with a P0506 code?
Only if running normally. A short trip to a shop may be reasonable if the light is steady and the car runs normally. Stop safely for a flashing light, severe shaking, overheating, loss of power, or another urgent warning. The code alone cannot confirm safety. Estimated repair: $50-$400.
How do I diagnose a P0506 code?
Work from evidence to part, not the other way round. A code names a circuit or a symptom; it does not name the part that failed. 1. Note every code that is set, not just this one. 2. Read the freeze frame — the conditions the fault was recorded under. 3. Confirm the fault is current rather than history. 4. Then work the likely-causes list in the order shown.
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