P0505 means the engine control module detected a malfunction in the idle control system that it does not classify as idle too low (P0506) or too high (P0507). On older engines with an idle air control (IAC) valve, it often means the valve is not responding to commands at all; on throttle-by-wire engines, it means idle is unstable or outside the module's authority in a way the low and high codes do not capture.
Severity: low to moderate. Can you keep driving? Yes. The symptom is a rough, surging, high or low idle and possibly stalling at stops. Nothing is damaged by driving it a short time, but stalling in traffic is the risk to manage.
What the bulletins point at
- Ford, 2005 to 2007 models (from Ford's submissions in a federal investigation into idle complaints): P0505, P0506 and P061B with idle fluctuation, corrected by reprogramming the PCM. Ford's explanation was that deposits build in the throttle body from normal crankcase ventilation and the original strategy did not compensate for them adequately. The fix was a calibration that learns around the deposits, plus cleaning.
- Jaguar Land Rover, 2019 to 2022 Range Rover, Range Rover Sport, Defender, Velar and F-Pace (technical topic AJ20-P6): idle instability, high idle, or P0505, P0506 and P0507, caused by crankcase ventilation breather membranes failing under mechanical stress and chemical attack from blow-by. The instruction is to fit the lower-level breather repair kit rather than the whole breather cover.
- Jaguar Land Rover 2013 to 2017 Discovery Sport, Evoque, XE and XF with the 2.0 L GTDi: a surging idle or P0505 after a previous repair that set the engine timing. The required action is to confirm mechanical timing with the proper locking tools; timing a tooth off produces an idle the module cannot control.
Three different mechanisms, and only one of them involves the idle system's own parts.
Causes, in the order they are found
A dirty throttle body or IAC valve that cannot meter idle air reliably.
A vacuum or crankcase breather leak, including a failed breather membrane or a PCV valve, adding air the module cannot control.
An IAC valve that is stuck or electrically dead on engines that have one; the module commands it and nothing changes.
A calibration that flags a normal idle or fails to learn around deposits, corrected by a flash.
Valve timing off after a timing belt or chain job.
A throttle position sensor or throttle actuator fault, usually with its own codes.
The module, last.
A diagnostic order
- Watch desired and actual idle on the scan tool, and how the IAC command or throttle angle moves as the module tries to correct. A command that changes with no effect on idle is a stuck valve or a leak; a command pinned at a limit is a leak or a restriction.
- Check the crankcase breather system for a failed membrane, split hoses or a stuck PCV valve; on the JLR engines above, this is the first check.
- Inspect and clean the throttle body or IAC valve, then run the idle relearn.
- Smoke-test the intake for leaks.
- Check for a software update for the vehicle.
- Confirm valve timing if the idle problem began after a timing repair.
- Clear and verify through cold and hot idle with the A/C cycling.
Frequently asked questions
Can I drive with a P0505 code?
Yes. The idle is unstable and may stall at stops, but nothing is damaged. Fix it soon to avoid a stall in traffic.
Is P0505 the idle air control valve?
On older engines with an IAC valve, often: a valve stuck with carbon or electrically dead cannot respond. On throttle-by-wire engines there is no IAC valve, and the causes are a dirty throttle body, a breather or vacuum leak, a calibration, or valve timing.
Why did P0505 start after a timing belt or chain job?
Because valve timing off by a tooth changes idle airflow and vacuum in a way the idle strategy cannot correct. Jaguar Land Rover documents exactly this on its 2.0 L GTDi engines after timing was set during an earlier repair. Confirm the timing with the proper locking tools.
How much does it cost to fix P0505?
A throttle body or IAC cleaning with relearn is under an hour. A breather repair kit or a PCV valve is an inexpensive part. A software update is an hour at a dealer. Resetting valve timing is several hours.
Related codes
- P0506 / P0507: idle lower or higher than expected; see P0506 and P0507.
- P0508 / P0509: idle air control circuit low or high.
- P061B: internal control module torque calculation performance, stored with P0505 in Ford's case.
- P0171 / P0174: lean codes from a breather or vacuum leak; see P0171 and vacuum leaks.
The code number itself tells you the family and the domain; how to read an OBD2 code number explains what each character means.