4.6L (1996-2004 Modular) Mustang Technical discussions on 1996-2004 4.6 Liter Modular Motors (2V and 4V) within.

Rough idle

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Old Jul 2, 2006 | 05:42 PM
  #1  
Gooman's Avatar
Gooman
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Default Rough idle

Hi nice site in here,I am new to mustangs and this site. Last week purchased a 99gt.The car runs great but has a rough idle at times.The car has 20600 mi on it and probably has sat for a while,I am running techron in the gas but need some advice,could the iac be bad or need cleaned? Thanks for any posts..........................Gary
Old Jul 2, 2006 | 05:44 PM
  #2  
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monkeydude3
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Default RE: Rough idle

try cleaning the iac, air filter, and the MAF. also look around and see if any vacuum lines are leaking, that will cause that
Old Jul 2, 2006 | 05:52 PM
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tommy_t
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Default RE: Rough idle

For sure check all your vaccum lines. I had the same problem, car stalled sometimes, idled rough, rpm's dipping below 500. Just when I was looking at my IAC I noticed I didnt plug in a vent hose when I removed my air intake a month earlier.......i felt so stupid.
Old Jul 4, 2006 | 04:58 PM
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GodAmGT00
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Default RE: Rough idle

You may also want to run some known good gas ALL the way through, as in, run 2 full tanks of gas through the engine, and if it still acts like sh-t, then start ripping sensors off....



My initial guess is bad gas... Also, try putting some Dry-Gas in the tank, it'll get rid of the moisture build up, especially if it sat for a while..



JT
Old Jul 5, 2006 | 02:37 PM
  #5  
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Default RE: Rough idle

i have a 1998 gt with the same problem but mine could be the plugs...there is one on the last cylindar that looks like it hasnt been replaced.......and if its not that it coule be the trigger which is a guess for me....also spray carb cleaner on the manifold and see if the engine kicks or any noise comes with that....but if it still has problems you will have some serious looking around to do
Old Jul 5, 2006 | 03:00 PM
  #6  
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LvGordo
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Default RE: Rough idle

Some people pay alot of money for cams to get that rough idle sound. I assume your car doesnt have cams. You got the sound for free!
Old Jul 5, 2006 | 03:23 PM
  #7  
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Phirantes
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Default RE: Rough idle

Most likely one of the problems already listed but just throwing it out that if the midpipe as been changed without proper calibration it can do the same thing..... idle rough, maybe even cut off sometimes.
Old Jul 5, 2006 | 03:28 PM
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Default RE: Rough idle

ORIGINAL: Phirantes

Most likely one of the problems already listed but just throwing it out that if the midpipe as been changed without proper calibration it can do the same thing..... idle rough, maybe even cut off sometimes.
related to that would be an exhaust leak before the front o2s, that caused me some trouble. usually the passenger side midpipe gasket will be the culprit if thats the case.
Old Jul 5, 2006 | 03:35 PM
  #9  
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From: Texas
Default RE: Rough idle

ORIGINAL: Gooman

Hi nice site in here,I am new to mustangs and this site. Last week purchased a 99gt.The car runs great but has a rough idle at times.The car has 20600 mi on it and probably has sat for a while,I am running techron in the gas but need some advice,could the iac be bad or need cleaned? Thanks for any posts..........................Gary
Try the cheaper things first. Someone said Dry-Gas or you could use SeaFoam ($5.99 at Autozone). Plugs could use a changing too...

GL
Old Jul 5, 2006 | 06:04 PM
  #10  
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Gooman
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Default RE: Rough idle

Thanks for the replys,great site fellerz...........................Gary



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