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Old 04-10-2018, 12:01 PM   #1
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Rough Idle, 2014 GT

I have a 2014 Mustang GT, any help would be appreciated, starting about 2 weeks ago my Stang has began to start sporadically idling a little rough. At idle, RPMS would drop to about 500 and car feels like it is going to stall and it bounces back up, the same happens when I put the car in neutral and coming to a complete stop, feels like there is a little vibration even at normal idle.

Driving and acceleration, everything seems fine. No engine light. Just under 32k and engine is stock. Car is DD and has about 4k since last oil change. So far, I cleaned the MAF and throttle body and it seemed to "fix" the idle for 2 days, and it's back to doing the same. Tried to capture it on video the best I can, but wasn't idling as rough today. First vid it around 8 sec mark and 2nd vid, idle seems to just bounce up and down a bit then drops and goes back to normal.
https://youtu.be/fxWrpMidomQ
https://youtu.be/w8NsMR9DLpQ

I went to check all the hoses and everything and I noticed the crankcase tube? has a crack in it. Looks like it happened from rubbing on the engine cover, looks like just the top part of the hose and not cracked all the way through to cause a leak. It also feels like there's a hard plastic tube under that hose, so I don't think it's leaking. Oil, plugs, any suggestions? Thanks
https://ibb.co/eB1Mrc
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Old 04-10-2018, 03:14 PM   #2
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Sounds like a vacuum leak, you can buy 5/8" hose for like 80 cents a foot. I'd remove that cracked factory line and put some regular 5/8" on it and see if it helps.
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Old 04-10-2018, 06:40 PM   #3
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I will try that, I actually ordered another replacement tube already. In the meantime, I used electrical tape around the tube, but still rough idling the same.
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Old 04-10-2018, 07:41 PM   #4
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i dont suppose you have a tuner / datalogger do you? 5 seconds and you would know if you have a leak or not by looking at your fuel trims.
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Old 04-10-2018, 07:47 PM   #5
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Starting fluid. You will find out if you have a vacuum leak.

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Old 04-11-2018, 06:23 PM   #6
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I don't have a tuner. Just forgot to mention, now that I noticed it more, the idle drops just right before the cooling fans turn on and then goes back to normal idle.
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Old 04-13-2018, 08:35 PM   #7
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take of the intake from the throttle body and clean the throttle body. this happened to me alot, might clear your problem asap. have someone sit in the car (while the engine is off) and step on the throttle, the blade will open up, clean around the throttle body and it should work fine. goodluck!
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Old 04-14-2018, 06:06 PM   #8
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If you still have the sound tube, get rid of it.
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Old 04-15-2018, 12:17 PM   #9
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Quote:
Originally Posted by alsabbagha View Post
take of the intake from the throttle body and clean the throttle body. this happened to me alot, might clear your problem asap. have someone sit in the car (while the engine is off) and step on the throttle, the blade will open up, clean around the throttle body and it should work fine. goodluck!
Yes, that was one of the first things I did, cleaned the MAF and throttle body, opened and around the flap too. "Fixed" the idle for like 2 days and it was back to the same.

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If you still have the sound tube, get rid of it.
Oh, that thing been yanked long ago when I got my exhaust.
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Old 04-15-2018, 06:05 PM   #10
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I don't have a tuner. Just forgot to mention, now that I noticed it more, the idle drops just right before the cooling fans turn on and then goes back to normal idle.
Just the cooling fans? Or is the air conditioning compressor also cycling on due to the ac/defrost functions being on?

These problems can be frustrating to diagnose. I would begin by testing the charging system, and scanning the PCM for any Diagnostic Trouble Codes. Even though the Check Engine Light is not illuminated, it is still possible that there is a pending code that may help with diagnosing the problem.
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Old 04-16-2018, 05:12 PM   #11
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Just the cooling fans? Or is the air conditioning compressor also cycling on due to the ac/defrost functions being on?

These problems can be frustrating to diagnose. I would begin by testing the charging system, and scanning the PCM for any Diagnostic Trouble Codes. Even though the Check Engine Light is not illuminated, it is still possible that there is a pending code that may help with diagnosing the problem.
Thanks, I will try to check if there is codes not showing. So far, it happens just when the cooling fans turn on and the car is warmed up to temp. I checked the battery/alternator, around 12v when not on, 14v when car turned on, and dips down to 13.8ish when I turn on the ac, headlights, and everything, and goes back to 14. Looks like that is all fine.

Cleaned the MAF and throttle body, replaced the crankcase tube, and so far, still the same. Only other thing I might try is throw in some Techron and see if that helps any. I guess only other thing is may be a vacuum leak.
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Old 04-17-2018, 08:13 AM   #12
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try to see if it is just dropping from the AC...make sure air flow is NOT to windshield (turns on ac!) then see if anything changes.

Also try idle re-learn by starting car and with everything off let it idle for 5 minutes.
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Old 04-26-2018, 06:57 PM   #13
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Yes, the idle drop has been happening with the air flow/defroster to front window. With everything off, there is still some rough idle, drops maybe 600, but not 500 where it feels like the car is about to stall, definitely not as noticeable. So what does it mean with AC on causing the idle to drop?

Also tried disconnecting battery and also doing idle relearn, still the same with the rough idle.
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Old 04-26-2018, 07:49 PM   #14
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Hi kanine,

You are kinda flying blind and by the seat of the pants here without a tuner and an understanding of how to use it. I can relate... I have one but I wouldn’t even trust myself to interpret a data log or live info. You (and even I) can however make good use of one as a code reader. You should consider investing in one (I actually have 4 code readers, one being an SCT X4 tuner). If your car has the tech/navigation package, you actually have a built-in DTC code reader that can clear DTC’s as well.

You should drop by an auto parts store and at least have them check for codes for free.

Ultimately, I suspect you’re going to need to take it to a good shop and pay for a diagnostic.
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Old 04-26-2018, 08:57 PM   #15
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I do have a scanner and checked, so far, not throwing any codes. Didn't try datalogging or monitoring yet, not sure the parameters. If I can't figure it out, I'll have it looked at next month when I take my car for servicing.
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Old 04-26-2018, 09:58 PM   #16
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Quote:
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I do have a scanner and checked, so far, not throwing any codes. Didn't try datalogging or monitoring yet, not sure the parameters. If I can't figure it out, I'll have it looked at next month when I take my car for servicing.
Good luck, and do post back with the final result. It helps us all.
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Old 05-08-2018, 04:40 PM   #17
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i dont suppose you have a tuner / datalogger do you? 5 seconds and you would know if you have a leak or not by looking at your fuel trims.
What would be the tell-tale sign in the fuel trims that signifies a vacuum leak?

This is good troubleshooting information that should be shared.
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