Some Idle Issues And Strange Noise

Discussion in 'SN95 4.6L Mustang Tech' started by 03_TrueBlue_GT, Jul 4, 2013.


  1. 03_TrueBlue_GT

    03_TrueBlue_GT Active Member

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    Hey guys lately my 2003 Mustang GT is having some issues with idling and has developed a strange noise. Earlier this week my SES light came on and I pulled the code with my programmer. It said the car was running to lean and you could tell because it was idling like it had a cool cam in it even though its stock. So I took apart the hoses to find a leak and found the hose connecting to vacuum part of the intake plenum was dry rotted out so I replaced it. Well it fixed the SES light and it idled normal after that.

    Now my current problem begins, the car drives great and has no issues when its moving but when I am stopped at a light or just idling the car has a strange idle. It idles at the normal 750rpms and then drops to 500rpms like its going to die but saves itself and continues to run, on top of this I have a strange noise coming from the left side of the engine. It makes this sound every so often and isn't continuous. It sounds like the car is struggling to breathe, and the noise is coming from inside the passenger fender I believe. I have taken the intake tube apart cleaned the MAF, cleaned the idle air control valve, replaced the fuel filter and checked for any issues with the rubber intake tube and found none. I have even done seafoam through the vacuum line and still the car makes the same noise and idle issue. I was wondering if it was my idle air control valve going bad but the noise isn't occurring from there. I got an ohm meter to check the ohms on the IAC but don't know what numbers are good and what are bad. I got from 13.5 to 26.5 on the IAC.

    I will try to upload a video to help show the noise because I cant describe it using words. Also the cars check engine light has not popped back up and my gas mileage has not been affected that much. Im just upset that my car is making this noise and strange idle that I cannot diagnose

    I thought about buying a new IAC but don't want to spend $100.00 dollars on a part that I don't need. I also thought about changing my spark plugs but they have under 30,000 miles on them and they are OEM Motorcraft plugs.
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  2. Mattstang04

    Mattstang04 Active Member

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    Did you try tapping on the IAC to see if it affected the idle? If it is sticking sometimes you can free it up a bit by rapping on it some. If it works, you know that's the problem. I took a leap of faith on mine when it started idling funny. Everything else operated perfectly. I gave the IAC a shot and it worked out for me. In addition, when mine went bad, the engine would idle so low that it would sound like it was gasping for air at times and never threw a CEL. Good luck.
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  3. 03_TrueBlue_GT

    03_TrueBlue_GT Active Member

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    Thanks for the tip Mattstang04! I went ahead and purchased a new IAC valve and took the leap of faith. Turns out it was a bad IAC and the car idles great now! Glad it was that cause it was $84 part!

    Btw your Mustang is nice, what kind of numbers are you putting out with that Procharger? The guy that tunes Mustangs in my area likes building Procharger kits for his customers a lot, reason why I ask.
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  4. 03_TrueBlue_GT

    03_TrueBlue_GT Active Member

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    Well the car is still having some issues.

    Now whenever I start it sometimes it will make a howling noise, when I apply the gas it goes away. Also when I am in 5th gear cruising around 50-65mph and put it in neutral the revs will hang at 2000rpms, or if I let off the gas and the rpms are at 1500 at 50mph the car will continue to go on its own, it doesn't build speed but maintains it. When I come to a stop from 55-60mph the car will hang the idle sometimes at 2000 and then fall to 500rpm and die while in neutral.

    This is beginning to be a real annoyance.
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  5. Jinx

    Jinx I like cats. Cats like me. Cats & I fully agree Cat Lover

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    Mine is doing the same exact thing (minus the howling noise). I noticed the symptoms only occur after the engine has past the 2000RPM mark while the vehicle is in motion. I am taking mine into Ford on Wednesday because mine will actually accelerate to a PCM determined speed without the pedal being pressed.
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  6. runningONfumes

    runningONfumes Member

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    TrueBlue... check your TPS. Ours are non adjustable and won't throw a CEL right away. As for the noise make sure all your air intake tubes are sung.
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  7. wmburns

    wmburns SN Certified Technician

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    IMO the likely cause is there still is a vacuum leak.

    But not a bad idea to clean the MAF.

    Also check the fuel rail pressure sensor intake vacuum reference line. Is it connected and leak free? Is there any evidence of raw gas in the line? If so, the FPRS is bad.

    Once you are POSITIVE there aren't any vacuum leaks, then look at the TPS as a possible cause. I'm doubtful because a bad TPS usually has an idle around 1200 RPM. A 2000 RPM idle likely means additional air from another source.

    Has the PCV value been replaced? Are all of the vacuum lines in good shape?

    With most IAC/Idle problems the trick is to find out WHERE the air is coming from.

    Here's some more information on how to trouble shoot idle/IAC issues.

    http://www.stangnet.com/mustang-forums/resources/troubleshoot-iac-idle-problems-1996-2004.13/
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  8. 03_TrueBlue_GT

    03_TrueBlue_GT Active Member

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    Update!

    I went ahead and returned the iac valve that I bought fromAdvance Auto Parts. I went to the stealership and bought a motorcraft IAC valve and the car runs like it should now. Thanks for all the help with this problem guys!
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  9. Mattstang04

    Mattstang04 Active Member

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    Glad to hear you got her fixed up. My car puts down about 370 to the wheels with a safe conservative tune. When I make a few more supporting mods, I will try to crank the number up a little more. I love my ProCharger setup.
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