Hard Start

[Tazman]

My truck had been running great lately till I went to start it two days ago.It would not start.I could hear the pump it just would not fire.I pumped the pedal and it started but I had to keep my foot on the pedal.I increased the idle via the idle screw and it worked fine.Then the next day the idle seemed very high so I lowered it back down.My question is why ,I did check the tps and the low side was high at 4.5 when I moved it to wide open it went to way past than normal.Is the TPS bad?Thanks 

[Lt.Del]

is this for a 87?  it would be TBI then right?
There is an idle valve that may be messing up. it's called an IAC (idle air control) valve.  Search this site or search youtube.com and find out how to test...they get dirty.  Carb spray works wonders.

[Tazman]

Yes it has an IAC which I did change two months ago.I still have the old one so I will check that out next.Thanks

[VileZambonie]

Do not mess with the idle stop screw. There is no idle speed adjustment. If you are saying the tps is reading 4.5volts with the throttle closed yes it is bad. Key on engine off at the signal wire you should have .5V throttle closed to 4.5volts wide open throttle with the voltage steadily increasing as you open it. Any OL or voltage spikes indicate a faulty TPS.

[Tazman]

Pulled the IAC and found the pintal end had come off the post.I had just put that in two months ago,exchanged it and the truck is back to running great.I will check the TPS again though.Thanks