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Erratic Idle on a 2001 3.8 Auto with 130,000 miles

Discussion in '1994-2004 V6 Mustang Tech' started by Joel Farewell, Mar 7, 2020.

  1. Joel Farewell

    Joel Farewell New Member

    Mar 7, 2020
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    Hi All,

    Here recently I have noticed the car is all over the map when it idles. So far it has yet to do these when the car is cold, but only after the car has been driven to operating temp.
    • In park, idles anywhere from 1000 to 1500 RPM, then suddenly drops to ~500 RPM, nearly stalling in the process, before returning to normal idle. It will do this in cycles
    • Occasionally will try to accelerate while stopped in Drive
    • Idles rough when stopped in Drive, not quite misfiring, but also not nearly as smooth as it should be
    • Has been consuming noticeably more gas
    Reading other posts about similar problems, it seems the main potential culprits are:
    • Vacuum leak
    • MAS
    • TPS
    • IAC
    It is also worth noting that I did have to replace the IMRC module once before, but it sounds like that is more of a power curve modifier than and idle control device. The car has not thrown any codes as of yet, so I am at a loss as to what exactly is the issue. I am going to start with searching for a vacuum leak and a new MAS, and slowly work towards the heart of the motor. I am hoping that someone has had similar problems and can point me in the right direction.
  2. six gun

    six gun Active Member

    Jun 26, 2014
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    South Dakota
    All good places to look, but see if you can't first hook a scan tool up first to see if there are history or pending codes for anything pertaining to it.

    You can carefully clean your existing mass airflow sensor with a q-tip sprayed with airflow sensor cleaner, or in a pinch brake cleaner before deciding to buy a new one.

    Checking for broken vacuum lines is also a great idea.