PO507 iat rpm higher than expected

I put a 5.3 in my 1992 pickup 2wd 5 speed with a stand alone harness cable driven throttlebody.Every time i start it cold or hot it will idle up to 1500 rpm back down to 700 back up to 1500 then back down and idle fine.i put a new throttlebody and sensors with no change.I sent harness and computer back so they could test on there motor and they are having the same problem even when they changed computer and another wiring harness.I think it is in there wiring harness both built by the same person but i would like to get your opinions.

Thanks Joe

Any clues!!!

Who built the harness?

Just chevy trucks made from donor harness.

Just to let everyone know my problem ended up being coil pack on #8 cylinder.I checked all my header temps and found #8 was 100 degrees cooler.Replaced coil pack and truck runs like a new truck.

thats strange, no misfires. plus u sent the harness and computer back and they are having the same problem. so i guess they need a #8 coil too?

Quote:

---

Originally Posted by gagliano7

Just to let everyone know my problem ended up being coil pack on #8 cylinder.I checked all my header temps and found #8 was 100 degrees cooler.Replaced coil pack and truck runs like a new truck.

---

Not trying to be a prick but if the company you're dealing with cant figure out that their #8 coil pack is bad on their test motor and thus cant help you resolve your issue... id be switching harness builders/tuners. I mean it sounds like theyre somewhat lackadaisical... nelson performance is awesome!

There # 8 coil wasnt bad mine was.They had the same problem with the idle i had.Those guys have been the best guys i have ever dealt with.They always answered the phone and helped me with any questions i had.I have heard great things about Nelson but they are to far away for me to deal with them.