I took my truck out one day to go get some crap for our wedding. When I started it up at the tux rental place it ramped up to 1700 rpm and stayed there, I spent the remainder of the day taking off with no gas pedal and all clutch. I adjusted the idle screw on the throttle body back down to 700 rpm and then goosed the throttle. When I did that, the engine revved up and then back down normally, only when it came down it kept going, the oil pressure dropped to 0, the check engine light came on, and then the engine sputtered up to normal idle again. I fine tuned the idle a little bit, and then tried it again, all good...for a minute. The engine then ramped up to about 1500 rpm when I restarted it and stayed there for about 30 seconds. then it came back down, but won't go below 1000 rpm. Every time I start it now, it stays at 1500 or higher for about 30 seconds then goes down to a constant idle of 1000 rpm. what the heck is going on? I'm afraid to mess with the idle anymore cuz I'm tired of it not doing what I was aiming for. It's a 90 F-150 I-6 300 CI 5 spd

 

<i>I adjusted the idle screw on the throttle body back down to 700 rpm and then goosed the throttle.</i>

That is not a idle adjustment screw, it is a stop screw to keep the throttle plate from digging into the throttle body. You need to set it back to exactly where it was before you turned it. So the plate fully closes but does not touch the throttle body's opening.

Idle speed is controlled by a IAC, and it is <u>not</u> adjustable you need to clean or replace it to correct the problem if you do not have a vacuum leak that is doing it.

 

IAC and TPS... normally LOW idle andstalls is the IAC but high idles is the TPS sensor.. and chek for codes

 

IAC - Idle Air Control
TPS - Throttle Position Sensor

Check Ford Fuel Injection for details on these units.

Could be either one, could be both. Make sure you put that stop screw back to where it was.

 

thanks all