Intermittent high idle

[Brettlance]

Have a weird one here. Have a 2017 Mustang GT 6 speed with about 22k on the odometer. The car normally idles around 650 rpm or so, which is normal. However, very intermittently, and typically after driving at low speeds, the car will idle up to around 1500 to 2k+. The CEL has previously thrown code p0507, which hints at a vacuum leak as other codes are not present. I've tried checking for vacuum leaks at the manifold and injectors, but everything seems fine.

The most recent work performed was an oil change and air filter replacement. I did tighten up the junction between the intake and the manifold previously to fix a vacuum leak, and I have pulled the battery terminals to clear the KAM.

Any ideas? The engine is entirely stock with the factory tune.

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[Mary Virgin]

Have a weird one here. Have a 2017 Mustang GT 6 speed with about 22k on the odometer. The car normally idles around 650 rpm or so, which is normal. However, very intermittently, and typically after driving at low speeds, the car will idle up to around 1500 to 2k+. The CEL has previously thrown code p0507, which hints at a vacuum leak as other codes are not present. I've tried checking for vacuum leaks at the manifold and injectors, but everything seems fine.

The most recent work performed was an oil change and air filter replacement. I did tighten up the junction between the intake and the manifold previously to fix a vacuum leak, and I have pulled the battery terminals to clear the KAM.

Any ideas? The engine is entirely stock with the factory tune.

Based on the symptoms you described, the high idle speed and the P0507 code, it is possible that the issue is related to the Idle Air Control (IAC) valve. The IAC valve controls the idle speed of the engine by regulating the amount of air that bypasses the throttle plate. A malfunctioning IAC valve could cause the engine to idle too high or too low.

One possible cause of the P0507 code is a dirty or malfunctioning IAC valve. Over time, the valve can become clogged with dirt and carbon deposits, preventing it from operating correctly. Another possible cause of the high idle is a sticking throttle plate or a vacuum leak.

Here are a few steps you can take to troubleshoot the issue:

1. Check the IAC valve: Remove the IAC valve and inspect it for dirt or other obstructions. If it is dirty, clean it with a carburetor cleaner and reinstall it. If it appears to be malfunctioning, it may need to be replaced.
2. Check the throttle body: Inspect the throttle plate for any signs of sticking or binding. If it is dirty, clean it with a throttle body cleaner. Also, inspect the throttle body gasket for any signs of damage or wear.
3. Check for vacuum leaks: Use a smoke machine or propane torch to check for vacuum leaks around the intake manifold, throttle body, and other areas of the engine. You can also use a vacuum gauge to check for leaks.
4. Check the PCV valve: The PCV valve regulates the flow of crankcase gases. If it is clogged or malfunctioning, it can cause the engine to idle too high. Inspect the valve and replace if necessary.

If these steps do not resolve the issue, it may be necessary to take the vehicle to a mechanic or dealership for further diagnosis.

 

[Cobra Jet]

Mustangs have not had IAC’s since 2004 because the idle is controlled through throttle torque management via the ECU.

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Go over your entire air intake hose tract…. Get some EFI specific throttle body cleaner. While the engine is at idle and safely parked, spray a little cleaner at the hose junctions, if the idle raises you have found your vac leak. Same is true with spraying it around any vac hoses on the intake.

Idle fluctuations can be caused by:
- MAF sensor (this can be cleaned ONLY with specific EFI MAF cleaner, do NOT use any carb cleaner or other caustic products).

- VCT solenoids - if the solenoids are not operating properly due to debris or they are failing due to age, they can cause such codes. Quite a few threads on here about these prematurely failing and/or how to diagnose.

This most recent thread, the culprit was the VCT solenoid::
https://www.mustang6g.com/forums/th...s-and-cam-retarded-codes.176734/#post-3571964

Here's (2) more threads for VCT info that I had previously posted in other threads:
https://www.mustang6g.com/forums/threads/2015-2021-s550-5-0’s-ssm-50067-vct’s-again-various-dtc-codes.169419/

https://www.mustang6g.com/forums/threads/p0018-code.123932/


- Throttle body (again, get EFI specific throttle body cleaner and clean the TB as per the directions on the can. Do NOT use any carb cleaner or other caustic products, as the TB has special coating that can be ruined if using anything other than EFI TB cleaner.).

Have you checked for any stored codes? If so, were there any and what were they?

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