Intermittent rough idle and greyed out auto start/stop most the time?

2016 FORD FOCUS
63,000 MILES • 2.3L • 4 CYL • TURBO • 4WD • MANUAL
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SKYLAR GEE
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Most the time when idling it idle hunts. But when warming up is when it goes from 1,200 to 1,000 RPMs just up and down. Then when it drops after a minute or so it'll drop to 500 RPMs then go to 800 RPMs back and forth. Carmax replaced the battery, fuel pump, throttle body, spark plugs and fuel pressure sensor but no luck. No codes in Forscan. But the auto start/stop also only turns green sometimes.
Aug 26, 2024 at 3:33 PM
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JACOBANDNICKOLAS
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Hi,

It sounds like a lot has been done. As far as the idle issue, have you checked for engine vacuum leaks or issues with the intake manifold tuning valve?

Let me know. Also, I need to know if you have access to a live data scan tool. Without specific codes, we need to be able to watch how different things react.

Let me know.

Joe
Aug 26, 2024 at 7:21 PM
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SKYLAR GEE
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I haven't checked for vacuum leaks because there isn't a loss of power. Still drives fine. Just didn't think that would be it.
Aug 27, 2024 at 10:27 AM
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JACOBANDNICKOLAS
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 110,190 POSTS
Hi,

An engine vacuum leak can certainly cause a rough idle. Also, once off idle, it may run perfectly.

Take a look through this link and let me know if anything appears to mirror what you experience.

https://www.2carpros.com/articles/automotive-engine-vacuum-leak-symptoms

Let me know.

Joe
Aug 27, 2024 at 6:47 PM