Engine

P1506 — Idle Air Control Overspeed: Idle RPM Above Target

Severity: low Safe to drive

What P1506 means

The engine control unit holds idle speed by adjusting the amount of air that bypasses the closed throttle, using the idle air control (IAC) valve. P1506 is stored when the unit commands the IAC to reduce air but idle RPM stays above target. This usually means extra air is entering the engine outside of the unit's control, or the valve is stuck open.

Symptoms

  • High idle in park or neutral
  • Surging or hunting idle
  • Harsh shifts or lurching when coming to a stop
  • Poor fuel economy
  • Check Engine light on
  • Occasional stalling when stopping

Possible causes

  1. Vacuum leak in the intake or vacuum hoses
  2. Stuck or sticky IAC valve
  3. Dirty throttle body
  4. Leak in the PCV system, hoses or valve
  5. Damaged IAC wiring or connector
  6. Throttle plate not fully closing

How to diagnose

  1. Read all codes and freeze frame data, and note any other faults
  2. Inspect vacuum hoses, intake ducts and PCV hoses for cracks and loose fittings
  3. Test for vacuum leaks with a smoke machine, or carefully spray carb cleaner around joints and watch for an RPM change
  4. Inspect the throttle body and IAC passage for carbon buildup
  5. Check the IAC connector and harness for corrosion, breaks or shorts
  6. Measure IAC coil resistance and compare with the manufacturer's spec
  7. Use a scan tool to see whether idle RPM responds to IAC commands
  8. After repair, clear the code and perform an idle relearn

Common fixes

  • Replace cracked vacuum hoses or leaking gaskets to stop the leak
  • Clean the throttle body and IAC passage with throttle body cleaner
  • Replace the IAC valve if it sticks or its resistance is out of spec
  • Replace the PCV valve or hoses
  • Repair the wiring or connector
  • Perform a throttle and idle relearn procedure

P1506 on different brands

Ford · manuals
Idle air control overspeed error: the module saw idle RPM higher than commanded.
Hyundai · manuals
Idle speed control actuator signal, coil #1, is above the expected range.
Jaguar
Idle RPM with the IAC valve operating is lower than expected for current conditions.
Kia · manuals
IAC valve opening coil signal is above the expected range.
Land Rover
A fault in the IAC circuit or function flagged as value high; the code points to the component, not one specific failure.
Mazda · manuals
Overspeed error in the idle air control system.
MINI
Idle speed control valve open solenoid control circuit signal is high.
Mitsubishi
Idle RPM with the IAC valve operating is lower than expected for current conditions.

Questions and answers

What does P1506 mean?

It means the engine computer cannot bring idle speed down to its target. The usual culprits are a vacuum leak, a dirty throttle body or a stuck IAC valve.

Can I drive with P1506?

Usually yes, but get it fixed soon. A high or surging idle hurts fuel economy and can lead to stalling.

Will cleaning the throttle body fix it?

Often, if carbon buildup is the cause. Check the vacuum hoses and PCV system first, though, since cleaning will not help if air is leaking in past the throttle.

This is general information about the code. The meaning can differ between makes and models: a scan tool and the repair manual for your car will show the exact cause.