I came across this TSB while searching for more information on the Ranger High Idle Problem. I don't see why this TSB can't apply to other year models but here it is.
High Idle TSB 00-3-5
00-3-5, Publication Date: JANUARY 31, 2000
1998-99 TAURUS SHO
A high idle may occur on some vehicles. This may be caused by a poor electrical connection at the wire harness (-12B637-) to Throttle Position Sensor (TPS).
Splice into wire harness (-12B637-) just after the TPS with TPS Connector High Idle Service Kit. Refer to the following Service Procedure for details.
Verify the concern vehicle exhibits a "high idle" condition when depressing the clutch or shifting between gears for the Ranger or when shifting between Park and/or Neutral for Taurus SHO. If high idle condition is not exhibited, proceed with other driveability diagnostic fix procedures. If condition is present, obtain a High Idle Service Kit (XF1Z-15K607-AA) and proceed by following the instructions found within the service kit.
OTHER APPLICABLE ARTICLES: NONE
WARRANTY STATUS: Eligible Under The Provisions Of Bumper To Bumper Warranty Coverage And Emission Warranty Coverage
Depends...800-1200 is usually about normal on my rangers. This TSB is for the surging idle that occurs when you are shifting between gears or coming to a stop light/sign and your idle jumps to 2500-4000 with the clutch in. Does the same for an automatic but I notice it more since I have a manual.
Some of your "high-idle" conditions are occuring probably because your temperature gauge sending unit is malfunctioning and sending a cold signal to your ECU. Therefore, the ECU is interpreting it as being a cold motor and needing to richen the mixture and raise the idle to speed the warming up of the motor. I replaced mine and the thermostat and it fixed my problem on my 93.
I have a 94 4.0 5sp and have the high idle problem. I have changed the TPS and the IAC and it still had the problem. We did some trouble shooting and it seems that there is a wire problem down someplace in the wire loom. Anyhow I have disconnected the IAC and it runs just fine. With or withouf AC on it idles around 800 rpm.
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