Question about 2004 Ford F150

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F150 Rough Idle when A/C compressor turns on

I have recently been having problems with my 2003 V6 F150. When the truck warms up, with the truck in gear (drive), and the A/C is turned on, the idle surges. Not enough to make the engine die but it is a pain to feel the truck vibrate as the idle is trying to stabilize between 600 and 800RPM. Checked the TPS, it is dead on -0.91V at closed throttle which is exactly what my ford mustang measures around the same year, and consistently is at the voltage when the engine surges. I have found that so many things can affect the idle on a V6 that it has become a headache. There are no vacuum leaks, checked with carb cleaner. Replaced PCV, DPFE, and spark plug wires. It only has this problem when the IAC compensates for the added load of the Air conditioner. Checked the voltage on the IAC Engine off key on 11V, 10.6 ohms across the IAC. If the truck hasn't been driven for a few minutes, it doesn't have this problem. Only after I have been driving it for a while does the idle surge when I come to a stop. Not sure what else to check. Has anyone had this problem before?

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  • a_voc Oct 30, 2008

    Try testing the fuel pressure and/or replacing the fuel filter.

  • a_voc Nov 03, 2008

    Dah, trying checking the voltage on the IAC. When in park no A/C -1.3V, when A/C on -3.4V, when A/C on in drive -4.86V. If voltage bounces around at -4.86, replace the IAC.

  • a_voc Jan 09, 2009

    EGR man get a clue

  • a_voc Mar 02, 2009

    Wasn't the EGR. The whole time the problem has been gas flow. So I had a clue, it wasn't the EGR.


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SOURCE: 2002 Ford Escape (V6) P0401 P0402 nightmare

Sounds like you have a vacuum leak, a problem with the wiring, or a bad PCM. Check wiring for pinched, chafed, pierced, or broken wires. Make sure vacuum supply is good, and not collapsing when the vehicle is running. Beyond that, a trip to the dealer may be in order.

Posted on Jul 22, 2009

  • 532 Answers

SOURCE: My 1996 Ford F150 4.9l 5spd. rough idle, poor drivability, stall

try replacing the throttle position sensor

Posted on Oct 24, 2009

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SOURCE: what causes 2000 taurus engine rough idle but no codes

remove neg. cable from battery so the ECM will reset this may work. make sure the IAC is air tight. if this doen't fix your problem have someone check the IAC valve if it's bad the part runs $300.00 pluse

Posted on Nov 25, 2011

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