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Old 10-02-2010, 11:08 PM   #1
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SLOW IDLE RETURN

I have a 98 mustang gt that the idle comes down slow. Any ideas what this might be.
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Old 10-02-2010, 11:28 PM   #2
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Re: SLOW IDLE RETURN

You mean it drops RPM's very slow after revving it?
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Old 10-03-2010, 07:39 AM   #3
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Re: SLOW IDLE RETURN

YES
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Old 10-03-2010, 12:29 PM   #4
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Re: SLOW IDLE RETURN

Idle Air Control Valve or Throttle Position Sensor. Clean your throttle body first.
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Old 10-03-2010, 05:45 PM   #5
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Re: SLOW IDLE RETURN

I sprayed the throttle body but didnt help.
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Old 10-03-2010, 06:57 PM   #6
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Re: SLOW IDLE RETURN

i just put a new idle control valve on but didnt seem to help much.
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Old 10-03-2010, 08:01 PM   #7
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Re: SLOW IDLE RETURN

Seafoam through the vacuum intake line.
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Old 10-03-2010, 08:37 PM   #8
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Re: SLOW IDLE RETURN

Do you mean the sea foam fuel additive or the sea foam spray for loosining bolts.
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Old 10-03-2010, 10:24 PM   #9
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Re: SLOW IDLE RETURN

This stuff. It's not just a fuel additive. It can be put in the crankcase, vacuum lines, fuel lines, etc. I run it through the vacuum by letting the vacuum line suck it out of the can a little bit at a time while holding the throttle open. Try it and see how it works.

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Old 10-04-2010, 06:54 AM   #10
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Re: SLOW IDLE RETURN

WHICH VACUUM LINE.
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Old 10-04-2010, 10:53 AM   #11
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Re: SLOW IDLE RETURN

maf needs cleaning, iac needs cleaning/replacing, or the idle decay rate in the ecu is high (but it wouldnt have just started if it was this). Ive heard good things about sea foam as well
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Old 10-04-2010, 11:13 AM   #12
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Re: SLOW IDLE RETURN

It always either the TPS or IAC ... The IAC can make the car run really rich too. It doesn't hurt to do the Seafoam or clean the MAF but I doubt these correct the problem
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Old 10-05-2010, 06:45 AM   #13
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Re: SLOW IDLE RETURN

I have been hearing alot of mustangs doing this i was told it was normal something to do with pollution control.
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Old 10-05-2010, 07:41 AM   #14
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Re: SLOW IDLE RETURN

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I have been hearing alot of mustangs doing this i was told it was normal something to do with pollution control.
If it seems to hang up or take extremely way to long then it's not normal. It should drop about 500-1000rpms in a second or less continuously
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Old 10-05-2010, 07:47 PM   #15
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Re: SLOW IDLE RETURN

i replaced both sensors and no change.
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Old 10-05-2010, 08:35 PM   #16
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Re: SLOW IDLE RETURN

Does it do anything else? Such as drop and rise in RPM's by itself while at idle? If it does that too, then you definitely have an exhaust leak. Check every hose and intake/vacuum line under the hood.
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Old 10-05-2010, 08:37 PM   #17
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Re: SLOW IDLE RETURN

no it idles perfect NO PROBLEM THERE.
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Old 10-06-2010, 11:57 AM   #18
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Re: SLOW IDLE RETURN

Do you have a stock throttle body?

And did you clean the throttle body?
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Old 10-06-2010, 12:13 PM   #19
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Re: SLOW IDLE RETURN

Stock throttle body and yes i cleaned it with sea foam.
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Old 10-06-2010, 10:31 PM   #20
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Re: SLOW IDLE RETURN

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Stock throttle body and yes i cleaned it with sea foam.
Get a towel or napkin or something and manually clean the TB at the plate while your opening and closing it. Get some brake cleaner and take the TB off and clean it with that till it's like new.
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Old 10-07-2010, 06:49 PM   #21
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Re: SLOW IDLE RETURN

its clean and looks new. I THINK ITS JUST NORMAL.
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Old 10-08-2010, 08:34 AM   #22
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Re: SLOW IDLE RETURN

Is this your first Mustang?
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Old 10-08-2010, 11:40 AM   #23
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Re: SLOW IDLE RETURN

I had a 1988 lx but this is my first 4.6 gt.
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