High/erratic idle?

[Fukitol]

Hey guys, I'm new to the forum, thanks in advance for the help!
I have an 89 c1500, fresh 350 with a 5 speed. Have msd 6al box, motorvation stage 2 chip, mid length headers 2 1/2 in exhaust with no cats, tbi spacer , ultimate tbi mod, and new tps , iac and map sensors. I am experiencing high idle, erratic at times. Have checked for vacuum leaks and found none, changed the iac with another new unit even tried adjusting the plunger out further with the same results. After changing and adjusting both times it idled great for the first few minutes so I shut it off assuming it was fixed...wrong! Next time I started it the issue was right back. Anybody have any experience with this? Also have an aftermarket breather on it with flow through lid if that matters.

 

[Fukitol]

Also have a new fuel pump , tank and filter.

 

[Fukitol]

think I figured it out, I didn't know you could knock a plug out and set baseline idle, messed with that a lil and improved it so far

 

[Fukitol]

Well that only worked until the next time I drove it, took the Tbi completely off, made sure there were no leaks between either gaskets on the spacer, reset base again, tps is running around .74v. Again it ran fine for a few minutes, shutting it off , recranking several times, no problems. Took it on a trip today and it got progressively worse until the point of it idling at 1,500 rpm. Pulled over, jumped a&b terminals, unplugged iac and am currently running it like that. Any reccomendations?

 

[smdk2500]

Have you checked for air leakage around the throttle blade shafts?

 

[Fukitol]

No I haven't , not familiar with how too? Also, wouldn't it do it with the iac unplugged if it was leaking there?I will look into how to check them and post results, thank you for the advice

 

[smdk2500]

I cant remember exactly how to off the top of my head. I think there was a post some where on here I read that said how. I don't remember. It might if it is letting enough air past. There isn't a piece of debris in the IAC hole is there that is not allowing it to work properly?