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2014 Mustang beginning to idle rough

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Old 4/5/18, 06:19 PM
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2014 Mustang beginning to idle rough

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 happens in the beginning and second vid around 8 sec mark.



Third vid, RPMs does some wierd jumping up and down a bit.

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
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Last edited by kanine; 4/10/18 at 04:56 PM.
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Old 4/10/18, 03:23 PM
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is yours by any chance having a voltage drop also?

my 13 is doing the same thing you've explained, but i have watched the voltage and have found that the voltage will drop to about 10 or 11 or so and then bounce right back up and idle just fine.

i notice it mostly when my cooling fans turn on, noticed it a whole lot during the winter while running the heater. I cant figure out what's causing the voltage drop which is dropping my idle.
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Old 4/10/18, 04:53 PM
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Now that you mention that, yes, I noticed it too, right after the RPM drops the fans turn on. I don't have a Premium so no voltage guage, I'll have to check with a multimeter. Normal with car on should be around 14 I think, so 10 to 11 is a bit low. That sounds like it could be the battery or alternator, how long has yours been doing that?
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Old 4/11/18, 08:30 AM
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yep, 14 is what it should be. Mine has been doing that since about november of 2017.

I was thinking about the battery or alternator also.

Just to mention, I let it sit for 2 months and would start it each week just to let it run for a while, then yesterday i actually had to jump start it and the battery is only a year old. Though it has kept a charge since yesterday morning while ive been driving it for the last 2 days... so that might cancel out the alternator idea (atleast i hope) so maybe it could be the battery...

I dont have a premium either but i swapped the cluster and was definitely one of my favorite "mods" to my base gt.
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Old 4/11/18, 06:42 PM
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It may also be a dirty throttle body. Easy to remove and clean.
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Old 4/11/18, 09:42 PM
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i watched my voltage gauge tonight, its now reading 13.7 even while driving. it used to be 13.9 all the time, until it would drop and idle rough for a few a second of course.
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Old 4/12/18, 04:22 PM
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It's normal to have an rpm dip and a voltage draw when the electric fan kicks in.
Mine does it too.


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Old 4/13/18, 09:11 AM
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Could you have some dirty injectors? They will cause the car you idle rough, and drop the rpm's. I'm old school, grab you some Marvel Mystery Oil, and run a tank full. It will clean anything. Just a thought. Good luck.
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Old 4/15/18, 12:04 PM
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Originally Posted by Gabe View Post
It's normal to have an rpm dip and a voltage draw when the electric fan kicks in.
Mine does it too.


.
Yes, but not like this. It never started doing this till now, rpms dropping to 500 and shaking. I checked my battery, it is fine, around 12, with the car on, it goes up to 14, and then turning everything on, drops to 13.8 but goes back up, so that all seems normal.
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Old 4/15/18, 12:07 PM
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Originally Posted by SpectreH View Post
It may also be a dirty throttle body. Easy to remove and clean.
That was one of the first things I did, cleaned the MAF and throttle body, cleaned it with the flap open too. It sort of "fixed" the idle for 2 days, but it went back to doing the same after. There was a little carbon build up, but wasn't that bad. I think I'm going to try some fuel system cleaner next, see if that does anything.
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Old 4/15/18, 02:10 PM
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Sounds like it might have a vacuum leak
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