Idle Air Control System RPM Lower Than Expected

What it means

The engine computer has seen actual idle speed stay below the target for a period, even while trying to add idle air. The most common cause is too little air getting in because of carbon in the throttle body, or extra load on the engine.

Related codes: P0505P0507P0101P0300

Symptoms4

• Low idle with noticeable cabin vibration.
• Engine stalls when stopping, when the A/C turns on or when shifting into gear.
• Brief hesitation when pulling away.
• Check engine light on.

Possible causes6

• Carbon buildup in the throttle body or idle air passage.
• Sticking or weak idle air control (IAC) valve.
• Clogged air filter or intake duct.
• Extra engine load from the A/C compressor, alternator or other accessories.
• Misfire or weak engine performance pulling speed down.
• Faulty electronic throttle body.

How to diagnose5

1. Compare desired and actual idle speed on a scan tool and watch the valve or throttle opening; a large opening with low speed points to a restricted air path.
2. Inspect the throttle body and air filter for carbon or blockage.
3. Turn off accessories such as the A/C one at a time and watch the idle change.
4. Check for misfire codes or mass airflow (MAF) sensor codes.
5. Test the idle valve and its wiring if the vehicle has one.

How to fix5

1. Replace a clogged air filter.
2. Clean the throttle body and idle air passage.
3. Fix any misfire or faulty accessory that adds load.
4. Replace the IAC valve or throttle body if proven faulty.
5. Clear the codes, perform an idle relearn, and confirm the idle holds steady with the A/C on.

Repair cost

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

A throttle body cleaning or new air filter is often enough; the upper end applies when the electronic throttle body is 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