i am trying to help someone fix his 96 ranger with the 3.0 , he had a cold start problem. the motor wouldn't idle until it was warm then it ran good. i checked the iac and cleaned it out , he went and bought a new tps sensor and replaced it, now the engine will idle very high then drop down low and this goes back and forth, with the tps when replacing it i was told you have to set it before you in stall it what does that mean? any help would be great

 

Does the check engine light come on? Here's a few links that might help:

http://www.allfordmustangs.com/Detailed/661.shtml

http://fordfuelinjection.com/tps.html

 

The TPS is simply a potentiometer. It will read less than 1.0V at idle, and max out at 5.0V when at WOT. There is no calibration to it. If you want to check the TPS, just backprobe it when the ranger is running. Grey/Red is ground, Grey/White is signal return, and Brown/White is the reference voltage. The reference voltage should be 5.0 +- 0.1V.


It's runs fine when it heats up because the HO2S sensors get up to operating temperature and take over the A/F ratio. It sound like it could be many things: vacuum leak, clogged TB idle port (did you drop anything at all into the TB when you replaced the IAC?), or a bad MAF.