Welcome To V6Mustang.com!

We are the oldest and largest V6 Mustang forum on the internet. If you have any questions about your V6 Mustang or just want to connect with other V6 Mustang owners around the world, you have found the best place on the internet to do that.

Registering is free and easy! Hope to see you on the forums soon!

silly high idle when engine is cold

Discussion in '1994-2004 V6 Mustang Tech' started by bluelionpiper, Oct 5, 2018.

  1. bluelionpiper

    bluelionpiper New Member

    Oct 5, 2018
    Likes Received:
    Trophy Points:
    Hey there,

    My 99 5 speed was doing great for the past year and then I road tripped it to Johnson city TN about 3 hours from me and when I got off the interstate the idle was about 2k. It ran great and throttle response was normal. Had my day and went back home and for that 3 hour drive it did great, other than I couldn't let off the throttle to slow down, almost always had to use brakes. When I got into town, I stopped for some food in a drive though and the coolant temp went over 210, but not by much. The next day she still idles really high but once she warmed up the idle drops to about 1k. That's been pretty consistent for the last week or so.

    I have unplugged the IAC, engine dies
    Checked for vacuum leaks, none that I can find and when I pull and vacuum line off the engine dies
    Haven't checked or messed with the TPS because throttle response has always been good
    Haven't messed with MAF

    Something changes from when the car is dead cold(70F) to when it starts to warm up(150F) that cause things to line up and the idle to drop.

    Could it be EGR? How would I test EGR? Something else?

  2. douglass

    douglass Active Member

    Aug 8, 2013
    Likes Received:
    Trophy Points:
    Bay Area, California
    If you have a way to data log you could see what the engine temp is reading when cold, and when it is hot.
  3. Joe Stein

    Joe Stein Member

    Jul 19, 2016
    Likes Received:
    Trophy Points:
    I would look at your coolant temperature sensor. Was your gas mileage decreased on your highway trip? Are you showing any CEL's? Good luck -