P0506Idle Control System RPM - Lower Than Expected
- Generic OBD-II code · Powertrain
- Turns on the check-engine light
- Matters for the ITP
- Needs a drive cycle to confirm a fix
- How the car detects it
- CARB requires the idle speed control to be monitored: petrol engines must flag a fault if the target idle speed is not reached within +200/−100 rpm, diesels within ±30 %. Older engines use a separate idle air control valve that bypasses the closed throttle; with electronic throttle the throttle itself controls idle and no separate valve exists. P0506 means the idle speed of the warm engine at standstill stays too low despite fully used control. GM uses more than 91 rpm filtered for 10 s (MIL after two trips), Ford petrol −100 rpm plus a correction above 1 lb/min, Ford diesel −100 rpm for 5 s, Subaru −100 rpm with the correction at its limit for 10 s three times. Typical are deposits, extra load or a restricted intake or exhaust.
- What you may notice
- Idle too low, engine shakes
- Engine stalls when stopping or with A/C on
- Check engine light after two trips
- Likely causes
- LikelyDeposits at the throttle or bypass channel, or gummed idle valve
- PossibleExtra load: stiff accessory drive, gearbox or converter
- PossibleIntake or exhaust restricted (air filter, catalyst)
- PossibleIdle valve or throttle actuator faulty, wrong learned value
- RareMechanical engine damage (low compression)
- Inspection (ITP)
- Matters for the ITP. While the check-engine light is on, the car fails the emissions check.
- Repair
- Medium · Often possible to do yourself.Typical cost: €30 – €600
- Related codes
Explanation from obdex (CC0), exactly as the app shows it. Guidance only; confirm with a workshop.