When I crank it back up it runs fine. If I get down on it though it will start idling high, so then I put it in neutral to turn it off and back on. Once again it runs fine after that.
^^^^This is a sign that the throttle is NOT returning to the SAME position each time the throttle is closed. Possible causes are:
- Broken/missing throttle return spring
- incorrectly adjusted idle stop set screw (either too high or low)
- Binding throttle linkage
- loose or worn throttle linkage
- loose TPS sensor. IE the sensor itself is moving.
- An incorrect speedometer can contribute to idle issues.
For the 96+ model year the PCM re-leans the TPS closed throttle value at each start up. The hanging idle occurs when the TPS value creeps up after start up. The problem clears up when the motor is shut off and back on because the PCM re-leans a new closed throttle TPS value.
To confirm this is your problem, monitor the TPS value with a VOM or monitor the TP-MODE PID with an ODB2 scanner. If using the VOM method, make note of the TPS value when the motor is first started. Compare the TPS value when the problem occurs.
For the ODB2 method, look at the TP-MODE PID to see if it's "P/T" (part throttle) when the idle is too high.
Then some checking for a vacuum leak should be done. A high idle value of 2500 RPM's is too high and may indicate a vacuum leak (assuming that the base problem isn't just binding throttle linkage).
See the following thread on how the TPS works and how to trouble shoot IAC/idle issues.
http://www.allfordmustangs.com/foru...ng-idle-idling-rough-post2260649.html#2260649
Bottom line: For correct idle determination the TPS must give the
SAME value
every time the throttle is closed.