This is my second visit to the site. My first was great with great response so thanks. Now I'm on to my 1993 F150 with a 5.0 FI. When I start it in the mornings and its cold out side all is well. When it comes out of High Idle, the idle becomes erratic. It will idle fine for a few seconds and then drop, most of the time will die. After driving the truck for a few minutes it seems the drop and die idle is less prominent but still happens once in a while. When it does idle, its smooth and when cruising down the high way its smooth and what a Ford should be. Just letting off the gas it will sometimes drop idle and sometimes die. Any suggestions would be appreciated.

 

I worked on an '86 that did the same when I picked it up so am assuming the TPS (throttle position sensor) is set up the same....
On that one the TPS voltage had to be within a certain range at idle, less than 1.0VDC but not too low. It was reading around 1.15VDC so the EGR was kicking on and off, fueling was adjusting for pedal being pushed, and basically it was using the IAC to chase its tail. Someone had already replaced the TPS once. For giggles I tried another one but it read the same.

Now, it was a pain to get setup because the voltage changed between key on engine off , and key on engine on due to the higher system voltage. I finally just reamed out the TPS's mounting holes with a small round file to make it adjustable and set it to around 0.8VDC or so with key on engine off, then with key on engine on it would jump up around 0.95VDC which was about where it needed to be. Oh, and if I remember right it was the green wire on the TPS that was the sending side and you can just use the engine for ground.

On the '86 it was a pain in the rear because the TPS was on the bottom and covered up pretty good so the throttle body had to be removed just to get to it. So of course it had to be removed, adjusted, installed, checked, turned off, removed, etc. I just cut the TPS sending line in the harness and wired in a test point so I could plug in my meter and leave it on while fooling with it instead of growing an extra set of hands.

On my buddy's '88 Mustang the dang thing is right on top of the throttle body and you can adjust it with the engine running almost in your sleep.

 

thanks for the help. I will look at that and let you know.