high idle in CL

[charger71]

I am dealing with a 99 JTEC controller truck idles fine while in open loop but as soon as it enters closed loop fueling it idles over 1k then fluctuates up and down till it comes back to 1k then climbs back up to 1300. Forgive my ignorance I am trying to get a hand on this JTEC platform so my question is what drives the idle during closed loop to change is it simply the IAC steps that are being changed during this time due to coolant temp factor or is there another input on idle for this that I am missing. I started this project with my daughter for her first truck and I am trying to get a grip on it do i need to focused on the dashpot idle air flow for this issue any information will be helpful thank you.

[Omunoz]

it sounds like a bad iac valve to me

[McCloud]

Agree, bad IAC or the ECT sensor is flaking out the engine is bouning RPMs based on mis-reported temps.