Idling

[Alexsam7620]

At stop lights or stopping , mustang starts idling and the rpm will fluctuate as if I’m revving the engine , sometimes it even shuts off it the idling too much . I have no mods fully stock

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[EFI]

Check for loose components in the air intake/manifold. Sounds like a vacuum leak.

The shutting off part is most likely a setting in the cars computer that shuts down the engine after half an hour of idling.

 

[KingKona]

....sometimes it even shuts off it the idling too much.....

That's normal.

Take of video of the tach at idle when it fluctuates.

 

[ORRadtech]

Lots of things can make the idle fluctuate.
Be more specific about when this happens. All the time? Occasionally? After a cold and/or a hot start? When cold? When hot? After a fill up?
The more detailed you can be the better our WAGs might be...

 

[sms2022]

There’s an idle relearn procedure but all the V8s I have owned with any camshaft fluctuate slightly at idle.

 

[Cobra Jet]

At stop lights or stopping , mustang starts idling and the rpm will fluctuate as if I’m revving the engine , sometimes it even shuts off it the idling too much . I have no mods fully stock

First, see if any error codes are stored. An S550 with varying idle characteristics could mean anything…. Could be the VCT’s, could be faulty IMRC in the intake, could be a vac leak (again could be intake related or something along the air intake tract is loose), etc.

It’s a gamble trying to “guess”.

Try the simple things first:
- see if any codes are present. If there are codes, post them up.
- If there are no codes, then check for vac leaks along the entire air intake tract, make sure all hose clamps are tight, make sure no tubing is loose or possibly broken, make sure air box is sealed, etc.. - If no vac leaks, pull the plugs and read them, see what their condition means.
- Clean the MAF; a dirty MAF or even loose connection at the MAF is known to cause idle/drivability issues.

Are you using some off the wall gas station fuel to save a buck?

 

[Alexsam7620]

At stop lights or stopping , mustang starts idling and the rpm will fluctuate as if I’m revving the engine , sometimes it even shuts off it the idling too much . I have no mods fully stock

- forgot to mention how I stop the car from idling at stops or lights is putting it in neutral and revving the engine and it stops

 

[Alexsam7620]

There’s an idle relearn procedure but all the V8s I have owned with any camshaft fluctuate slightly at idle.

I did have a camshaft positioning error code at one point but fixed it

 

[Alexsam7620]

That's normal.

Take of video of the tach at idle when it fluctuates.

I will take video of the next time it happenes and how it sounds

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