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

SKYLAR GEE

MEMBER
2016 FORD FOCUS
2.3L
4 CYL
TURBO
4WD
MANUAL
63,000 MILES

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.

Monday, August 26th, 2024 AT 3:33 PM

3 Replies

JACOBANDNICKOLAS

MECHANIC
110,114 POSTS

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

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Monday, August 26th, 2024 AT 7:21 PM

SKYLAR GEE

MEMBER
2 POSTS

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.

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Tuesday, August 27th, 2024 AT 10:27 AM

JACOBANDNICKOLAS

MECHANIC
110,114 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

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Tuesday, August 27th, 2024 AT 6:47 PM