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2004 4.6 Inconsistent Idle Quality

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  • 2004 4.6 Inconsistent Idle Quality

    My 2004 GT (4.6 V8) has a new problem. The idle quality is inconsistent. When first cold everything seems to be good. As it starts to warm up, and after completely warming up, sometimes the idle speed drops by about 100-150 RPM and the idle is rough. It's a stick shift car and I usually sit at red lights with the clutch out and transmission in neutral. I've hit the clutch when this happens to eliminate a problem with the transmission spinning in neutral. Clutch in or out has no effect on this idle problem. When the speed drops I hear a faint sound that reminds me of a bad wheel bearing. It could also sound like a vacuum door fluttering, if there is such a thing in the intake. The idle speed drops like I am slowly engaging the clutch without hitting the gas, but I'm not doing that. About three times so far the idle speed has dropped so low the engine died. I've seen the idle speed drop to about 300 RPM. The drop in idle speed only lasts 3 to 5 seconds when it happens.
    Any ideas before I take my car to my Ford dealer? The airflow sensor that is right behind the air filter has special "theft-proof" screws. I would need a special driver to replace that sensor.

    Tracy M&M #245
    Mac OS X/ Earthlink DSL
    2004 GT 5-speed
    1956 F-100 Panel w/429 (3.50 9")
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    Music City F-100's,
    1965 Holman Moody B/P "What if?"(2.78 1st & 3.70 TracLok 9")
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    Don't focus on the destination....make the JOURNEY the adventure
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  • #2
    Have you tried cleaning the throttle body and Idle Air Controller, that’s what I’d try first, assuming you aren’t getting any trouble codes. Be sure to get the type of carb/throttle body clearer that’s safe for sensors and such.
    '70 Mach 1 - '72 Sprint - '94 F-150 XL -'97 E-150 - '18 Edge SEL AWD

    My Mach's restoration progress
    My Sprint's restoration progress
    ”Mercy for the guilty is cruelty to the innocent.” ~ Adam Smith


    • #3
      I agree with Steve. I've had issues like that too, and it's typically due to air intake. Once I had a pin hole in the air intake hose, and the other was the air flow sensor that needed cleaning as Steve pointed to.
      It isn't an official project until you've bled on it!

      M&M Member #33
      '66 Coupe C code
      '01 Saleen S281SC #648


      • #4
        X3. Clean everything with sensor safe spray cleaner. You can get those theft proof bits now, Lisle carries them as do others. I bought a set to work on the last Vette I owned.
        ----1999 F150 XLT Lariat Super Cab 4X4 5.4----
        -----1947 Lincoln Zephyr Coupe 5.0-----
        -----2005 Expedition Eddie Bauer 5.4----
        " Sometimes you fix the car, sometimes the car fixes you" Steve L.

        "Do not let anyone tell you it cannot be done. No challenge can match the heart and fight and spirit of America". President Donald J. Trump