1995 K3500, (454), Computer commanding high idle...too high

[454/4X4]

I got this truck last week, just got a trans rebuilt and put in. It runs great, loads of power. But, it was idling at like 1100rpms, and thats hard on parts.

I did the usual stuff...i checked for vac leaks, found none.

I checked for air leaks at the TBI spacer/mount...nothing.

I cleaned the Throttle Body...no change

I removed and checked the IAC valve...was spotless.

I removed and checked the EGR..also spotless, no leaks.

Drilled the plug over the base idle screw and turned it out, but it made no change.

Put on a new IAC valve...came down to like..1000ish...So i removed the IAC and turned the pintle out 3 turns, and put it in...voila...idled at 650 in gear, 750 in park. I shut it down, cranked back up..and it went to 750....then 850..then 1000...ugh, no change.

So...I reset the computer...did a drive, and long idle, no change, still right around 1000 rpms.

Okay..so now I jumped the A/B terminal in the ALDL...key on, engine off...for 10 seconds, and unplugged the IAC. Jumper out, key on engine on...and it started, and idled at 700 in park...good smooth, strong idle. I turned it off, plugged in the IAC...and cranked it back up...idled great, I backed it out the shop, but after a couple minutes..it stepped right back up to 1000 again.

So...i dont know, the computer wants it to idle at 950-1050, no matter what....how do I change what the computer wants, on a 95?

 

[454/4X4]

Question...


If the computer is doing it s job, with bad info..what can cause it to want to idle too high?

 

[eg30.06]

throttle position sensor. happened on my 95 only mines a 350

 

[454/4X4]

I tested the TPS output at the blue wire, smooth sweep, it was .46v at idle and 4.54 at WOT.

i put on a good used ECU today, with a PROM already in it...cranked right up..idled down to 750...but the thing ran like crap from 1000 to 2000 rpms.

I swapped the PROM from my ECU into the new one, and it ran great, but once again...idled at 1000.

So, I have a bad PROM as best I can figure...

 

[454/4X4]

Called a local speed shop...they called JET performance and they said I need a new PROM...so, tomorrow Ill order a new PROM...Here's to hoping its not another 75 dollar waste of money.