Idle Air Control System RPM Higher Than Expected

What it means

The engine computer has seen actual idle speed stay above the target for a period, even while trying to reduce idle air. This usually means air is entering the engine without the computer controlling it, such as a vacuum leak.

Related codes: P0505P0506P0171P2111

Symptoms4

• Noticeably high idle after the engine warms up.
• Vehicle pushes forward when stopped in Drive.
• Occasional hissing sound from the engine bay.
• Check engine light on.

Possible causes6

• Vacuum leak from hoses or the intake manifold gasket.
• Idle air control (IAC) valve stuck open.
• Leak at the PCV valve or its hose.
• Leak in the brake booster hose or diaphragm.
• Throttle body not closing fully, or not relearned after cleaning.
• False coolant temperature reading making the computer think the engine is cold.

How to diagnose5

1. Watch the idle valve or throttle opening on a scan tool; a very small opening with high speed means air is entering elsewhere.
2. Check fuel trims; high positive values at idle point to a vacuum leak.
3. Have a smoke test done on the intake manifold and hoses.
4. Inspect the brake booster hose and the PCV valve.
5. Confirm the coolant temperature reading is plausible once warm.

How to fix5

1. Replace the leaking hose or gasket.
2. Replace the PCV valve or its hose if damaged.
3. Clean the throttle body and perform the manufacturer idle relearn.
4. Replace the IAC valve or throttle body if proven faulty.
5. Clear the codes and confirm the idle returns to normal after warm-up.

Repair cost

In Saudi riyals; the highlighted part is the expected range for this fault.

The fix is often a leaking hose or a relearn after cleaning at low cost; it rises when the electronic throttle body must be replaced.

Prices are rough estimates for common cars at independent workshops and vary with the car and the source of the part.
Prices last updated: September 2026

Frequently asked questions