Rough idle ONLY when A/C is ON. - Ford Mustang Forum
 
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post #1 of 10 (permalink) Old 07-19-2015 Thread Starter
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Rough idle ONLY when A/C is ON.

Ok so to set this up correct.

A/C OFF:
Car runs normal no idle issues

A/C ON:
When slowing down to a stop a stop light the RMP's fall to about 500 or just under then bounce between just under 500 and just over 750 RPM's until a few seconds after the car reaches a complete stop. Once it levels out and still stopped if you flick the gas peddle it will rev up then fall below 500 then level back out at 750 pretty quick like it should.

After having this issue (every time recently) I will shut the A/C off when about to slow down for another light and let the clutch out as normal and what do you know, no idle issue. So I know it has to do with the A/C being on.

Any thoughts?


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post #2 of 10 (permalink) Old 07-20-2015
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A dirty throttle body could be causing the idle issues so I suggest you clean it thoroughly especially between the blade and the bore.



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post #3 of 10 (permalink) Old 07-20-2015 Thread Starter
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Quote:
Originally Posted by Bullitt95 View Post
A dirty throttle body could be causing the idle issues so I suggest you clean it thoroughly especially between the blade and the bore.

Yeah, I have that on my to do list this week to clean the throttle body and intake sensors.

Just wondering though could a dirty throttle body effect the idle ONLY when the A/C is ON? Yet when A/C is OFF it idles normal?

Current Garage
(11.)2012 GT500 silver with red stripe, SVT performance package, and Recaro seats.
2018 Honda Civic Type R
Past Mustangs in order and color of text.
(1.)2000, (2.)2004, (3.)2006GT/Auto traded for (4.)2006GT/Manual, (5.)1996, (6.)2011GT, (7.)2003GT, (8.)2006GT, (9)2013 Boss 302, and (10.) 2002GT
(I have owned a few non Mustang cars over the years as well, but always try to have a Mustang with it or come quickly back to a Mustang!)
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post #4 of 10 (permalink) Old 07-20-2015
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Quote:
Originally Posted by MustangLife View Post
Yeah, I have that on my to do list this week to clean the throttle body and intake sensors.

Just wondering though could a dirty throttle body effect the idle ONLY when the A/C is ON? Yet when A/C is OFF it idles normal?
Hey MustangLife. Did you check for DTC codes. Do you still have the original T.B. I hade the same symptoms in 2010. Idle was erratic and low with A/C on. With A/C off idle was good. Ford said it had a code P0506 ( I.A.C value .9 out of spec. ) They replaced the T.B cleared the K.A.M and reprogrammed the P.C.M with a update. Never had a problem after. You know Ford they don't fix they replace. I'm not saying that's your problem but it sounds like the same thing.

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post #5 of 10 (permalink) Old 07-20-2015 Thread Starter
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Quote:
Originally Posted by night rider View Post
Hey MustangLife. Did you check for DTC codes. Do you still have the original T.B. I hade the same symptoms in 2010. Idle was erratic and low with A/C on. With A/C off idle was good. Ford said it had a code P0506 ( I.A.C value .9 out of spec. ) They replaced the T.B cleared the K.A.M and reprogrammed the P.C.M with a update. Never had a problem after. You know Ford they don't fix they replace. I'm not saying that's your problem but it sounds like the same thing.

Interesting. So your check engine light was on? It hasn't ever thrown a code since this has been going on. Guess I could hook it up to my friends scanner just to see if there is anything being stored similar to what you are saying.

I do have still have stock throttle body installed. All mods are in signature so if you see something that stands out that could be contributing to problem let me know.

Current Garage
(11.)2012 GT500 silver with red stripe, SVT performance package, and Recaro seats.
2018 Honda Civic Type R
Past Mustangs in order and color of text.
(1.)2000, (2.)2004, (3.)2006GT/Auto traded for (4.)2006GT/Manual, (5.)1996, (6.)2011GT, (7.)2003GT, (8.)2006GT, (9)2013 Boss 302, and (10.) 2002GT
(I have owned a few non Mustang cars over the years as well, but always try to have a Mustang with it or come quickly back to a Mustang!)
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post #6 of 10 (permalink) Old 07-20-2015
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Quote:
Originally Posted by MustangLife View Post

Just wondering though could a dirty throttle body effect the idle ONLY when the A/C is ON? Yet when A/C is OFF it idles normal?
absolutely, there is more load on the engine with the a/c on.

its most likely a dirty throttle body or a bad throttle postion sensor
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post #7 of 10 (permalink) Old 07-20-2015 Thread Starter
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That is a good point about more load. Well that is were I will start this week then.

Thanks. I will post back near end of week to follow up results. Hopfully positive ones! haha

Current Garage
(11.)2012 GT500 silver with red stripe, SVT performance package, and Recaro seats.
2018 Honda Civic Type R
Past Mustangs in order and color of text.
(1.)2000, (2.)2004, (3.)2006GT/Auto traded for (4.)2006GT/Manual, (5.)1996, (6.)2011GT, (7.)2003GT, (8.)2006GT, (9)2013 Boss 302, and (10.) 2002GT
(I have owned a few non Mustang cars over the years as well, but always try to have a Mustang with it or come quickly back to a Mustang!)
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post #8 of 10 (permalink) Old 07-21-2015
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Quote:
Originally Posted by MustangLife View Post
That is a good point about more load. Well that is were I will start this week then.

Thanks. I will post back near end of week to follow up results. Hopfully positive ones! haha
when ceaning the TB take it off the car so you can get behind and in front of the plates real good. and pay close attention to the pivot points on the sides, IMO thats the most problem prone area causing the sticking.

you can also try a throttle reset if the maintenance fails. i believe the procedure is in the owners manual and involve teaching with both the a/c off and then on.
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post #9 of 10 (permalink) Old 07-31-2015 Thread Starter
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Cleaned the MAF and that seemed to do the trick.

Current Garage
(11.)2012 GT500 silver with red stripe, SVT performance package, and Recaro seats.
2018 Honda Civic Type R
Past Mustangs in order and color of text.
(1.)2000, (2.)2004, (3.)2006GT/Auto traded for (4.)2006GT/Manual, (5.)1996, (6.)2011GT, (7.)2003GT, (8.)2006GT, (9)2013 Boss 302, and (10.) 2002GT
(I have owned a few non Mustang cars over the years as well, but always try to have a Mustang with it or come quickly back to a Mustang!)
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you should still do the throttle IMO.
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