IAC problems

[ssheets]

With my older 02 LS1 predator I'm limited on IAC tuning. My engine wants to occasionally idle up to 2-3k or when your driving through town it's like the cruise control is always on.

I unplugged the IAC and it drives much better. It just doesn't idle as well. It doesn't want to smooth out and surges between 850-1100rpm sometimes. I only tried this for about 10 minutes of driving, but it sure seems like it's the IAC.

Any advice or knowledge would be appreciated.

[santaman58]

Hey I had a similar problem with my corvette and it turned out to be a faulty TPS sensor. Intermittent high idle...1.5-2k rpm. Installed new one and fixed the problem. Its a reasonably priced item so might be worth a try. Just my 2 cents worth. Good Luck.

[ssheets]

Hey I had a similar problem with my corvette and it turned out to be a faulty TPS sensor. Intermittent high idle...1.5-2k rpm. Installed new one and fixed the problem. Its a reasonably priced item so might be worth a try. Just my 2 cents worth. Good Luck.

I'll keep that in mind. My scanner showed a TPS of 0% so I was thinking it was something else...I also just found that the throttle body screws were not that tight. Actually they were pretty loose. You couldn't hear any air sucking in, but it sure is suspicious. I'm going for a drive right now and see if made any difference. I remember now late one night setting the TB on the manifold thinking I was going to take it back off so I didn't tighten it. The next day we contined reassembling and I missed the bolts!!! Well, that's called shakedown tuning. If it runs better I'll swap PCMs and try the one that has the tune for my mods. This one is a modified Predator performance tune.

Wish me luck...these problems, while annoying, sure help the learning experience.

[ssheets]

That wasn't it. The throttle body wasn't torqued down, but those O-rings do seal well. It runs like crap still with the IAC plugged in. It starts fine, but driving is miserable as it hangs at 2k between shifts and when cruising it just does whatever it wants. I was going down the highway at 50mph without cruise control and without touching the gas!! Long story short, I unplugged the IAC and it runs great. Of course it won't idle right without it, but under all other conditions the car runs great without the IAC plugged in. My LTFTs are usually right around 0 and it's a blast.

What is the failure mode of the IAC? What worries me is it seems that this would more likely be an input driving the IAC and not the valve itself. It looks like the IAC is just a linear electric motor that would fail and get stuck in one position, not take on a personality

As I think back the car's idle or off the gas rpm always hung more than my other SS, but now with all the engine mods it's much worse and with the louder exhaust it is more noticeable. It's unsafe the way it is though, I wouldn't let my wife drive it if it may decide to cruise at 3krpm through town...which is 40-50mph in 4th or 5th gear.

Any thoughts on maybe a bad TPS switch too? My scanner reads 0 TP angle while this is happening so I kind of doubt it, but I'm not sure how these systems work together? I might be able to swap the IAC off of my Suburban and see what happens?

[ssheets]

Just did another hour of reading...it could be a tuning issue, but I can't do anything about it with just a Predator. Maybe Jesse at Wait4me can help me figure it out? If not, I think I'll buy some tuning software and learn how to fix it myself.

[ssheets]

Vacuum leak. Doh!!!!!!
Seems to be running great now.

[rletzgus]

Where did you find the leak? I am having some issue with my LS1 idling too. Maybe same thing, any info always good. Thanks in advance.