GM TECH ? (CRASH?) IAC issue?

Pook · Mar 15, 2010

My buggy is currently running very well, minus a random reoccuring often enough to be a real pain in the ass idle issue, once it warms up.

Originally there was a tuning issue with the motor not getting enough air at idle due to the larger cam. The tuning shop redid the tune and sent me the program and I loaded it up. It runs way better now but there still is an idle issue.

It sounds like the motor is gulping for air at idle, then suffocating, then gulping and some time stalling or it surges upward in RPM. All very randomly, you can hear funny electric motor sorta sound coming out the intake during these times...

I've got a check engine light on, and will scan it shortly, but I really think its the IAC...

Does this sound like it could be the issue? Can I just clean it and reinstall. The motor sat for awhile and the LS1 intake was bought on EBay so unknow history.

Specs on motor. Lowmileage 5.3, LS1 intake and injection, GM Hot Cam, fancy valve springs and stuff, Schwanke computer tune, no O2s, supposed to be pushing 425hp according to Schwanke. It has a 4" intake, KN filter with prefilter, and a LS2 MAF sensor thingy.

:beer:

deerlick · Mar 15, 2010

how is it controlling the fuel with no 02's?

Pook · Mar 15, 2010

Its a custom tune with fuelmapping thats was figured out on a Dyno. Lots of race cars, rock buggies etc, run this way.

crash2 · Mar 15, 2010

Fly by wire or cable?

Pook · Mar 15, 2010

Cable. LS1 intake and throttle body.

crash2 · Mar 15, 2010

Without seeing the fuel mapping/comanded iac counts its a shot in the dark what do to. Plus you are messing with a custom program for fuel management. Alot of variables...

Pook · Mar 15, 2010

I can bought the EFI live tuner program. I can pull all that info up and check it and mess with it if I wanted too.

I'll ran the scan on it before i go for lunch and see what code pops up.

Mostly wondering what the symptons on a gummed up or faulty IAC would be.

Pook · Mar 15, 2010

been told the IAC may be sticking or acting up, but also was told I may need to open up the hole in the butterfly valve a bit more to allow more air through due to the bigger cam and that the IAC might not flow enough or can't keep up.

JOOP · Mar 15, 2010

So basically it's hunting for the idle..

What's the voltage on the TPS at idle??

Binder · Mar 15, 2010

Pook said:
been told the IAC may be sticking or acting up, but also was told I may to open up the hole in the butterfly valve a bit more to allow more air through due to the bigger cam and that the IAC might not flow enough or can't keep up.

I'm not specifically familliar with the LS series engines but it does sound like the IAC may need to be adjusted. You can take it out and clean it but probably won't help. Dont turn the ignition on with the IAC out and plugged in.
As far as no 02's that's fine and that's how I do it too.

crash2 · Mar 15, 2010

From past experiances--- I have yet to have an IAC fail on those series of motors. One thing I have found and mostly on fly by wire is buildup around the throttle body causing low/dippidy idle conditions. Only seen it on a couple throttle cable versions.

best thing you can do is look at the comanded vs. actaul and thet will give you some sort of an idea. But I am going to guess its in the setup.

Pook · Mar 15, 2010

Setup as in the tune/programing?

Schwanke Engines, builds Dirt track race engines, and also does all the engine stuff for twisted Customs, does sealed spec class race motors, runs a full dyno tuning shop and are supposedly quite good at what they do. I'm pretty confident the tune should be right, I downloaded the current tune and emailed it to them to check and it they said it was good.

Pook · Mar 15, 2010

Crash it came up with the Code PO113.

Trying to find out what that is, could you look it up?

Pook · Mar 15, 2010

Air temp sensor Voltage high. So whats that mean? Sensor is garbage?

crash2 · Mar 15, 2010

Possably bad sensor but without checking the feedback voltage and what the pcm see's the feedback voltage is its just a guess.

Pook · Mar 15, 2010

man these fancy motors are a pain.

So is that something I can get out a good old voltmeter to read or I need to plug it in to the scanner and my laptop and fumble my way through this nice new program I got to figure out?

I want to learn this fancy new efi stuff, just busy with life and want this thing to run perfect for now :haha:

crash2 · Mar 15, 2010

Any idea what year the donor stuff is from chris?

t1h5ta3 · Mar 15, 2010

we had that issue on a camaro that had a big cam. if i recall we tricked it into closeing the iac, unpluged it, then set the base idle with the throttle stop screw to about 50-100 rpm below desired rpm, turned it off, reconected it, and restarted it. once warm it relearned and was fairly stable. got an ocational idle surge after snaping it shut from wot.

Pook · Mar 15, 2010

crash said:
Any idea what year the donor stuff is from chris?

The 5.3 is a 2004, not sure on the LS1 intake and TB or the LS2 MAF but will find out.

Thanks for the call back Crash.This GM stuff is a whole new world.

:beer:

skinny_pedal · Mar 15, 2010

Intake leak? Honestly putting it on some sort of computer and watching a graph is going to be your best bet. Like everyone else said it's just going to be a guess.