Erratic idle

2013 FORD MUSTANG
94,000 MILES • 5.0L • V8 • 2WD • MANUAL
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GTBEAST
  • MEMBER
  • 1 POST
When in neutral, the idle will drop to 400 and jump back to 1000 rpm. Sometimes it shuts off when this happens. It happens almost every time when the clutch is pushed in or sitting in neutral. My fuel mileage has also dropped but has no other drivability issues. There have been no check engine lights.
Apr 29, 2019 at 12:45 AM
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SCGRANTURISMO
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 4,897 POSTS
Hello,

This could be a problem with an air intake or a vacuum leak. An intake leak is described as any air leak entering the system after the Mass Airflow Sensor (MAF). A good way to find this is to get a propane torch. With your vehicle idling crack the torch open to it's lowest setting without igniting it, so just the propane is leaking out. Go around the air intake duct, throttle body, intake manifold, vacuum lines, and Evap lines. When the torch passes by the leak, the engine rpm's will pick up as the propane is ingested into the system through the leak and burnt in the combustion chambers of each cylinder. Replace the defective part ans you are done. I have also included a couple of links below for you to go to:

https://www.2carpros.com/articles/evap-system-code-repair
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Pleas go through these guides and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
Apr 29, 2019 at 1:30 AM
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BMDOUBLE
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 1,139 POSTS
I have had issues with the vct (variable cam timing) solenoids on these engines. Just did one a few months ago and it was extremely intermittent! I caught it by monitoring the vctadverr parameter on the scan tool. They should stay at or near 0% and the driver side one would flip out off the scale at times. This is only one possibility though so don’t replace it unless you are sure!
Apr 29, 2019 at 7:54 AM