IAC Test

[RDF1]

Have yall seen a Gen 3 PCM do a IAC test while idling?

Had a customer drop a car off earlier and its doing something strange.

Runs and drives great but while idling it will ramp the IAC up for about 2 minutes then fall back down and idle good till the IAC ramps up again.

Seems its going to the exact same IAC Position when this "test" is being run.

After digging i found a IAC Test going Enabled/Disabled when the idle starts climbing.
Smoke test the intake manifold and found no leaks.

Im not seeing anything in the tune that is just so far out of wack for it to do this.

He said he replaced the IAC a couple times with ACDelco and the throttle body with another stock TB.

Its got a nice Chinese low quality swap harness too. No oxygen sensor activity and its running in OL with lots of codes disabled.

Ill be able to get a DL and upload the tune in a little while.

[bk2life]

Gen 3 PCM do a IAC test

ive only heard of O2 tests

[Alvin]

occasionally they will reset LTIT and STIT back to zero. Just like fuel trims will reset to zero by themselves occasionally. That sounds like the issue.

[RDF1]

How often do you see that reset? Surely not several times in 10 minutes.
I cleaned the TB and IAC port. IAC is at 0 and idle is a little above target. But so far it hasnt done anything crazy while i have computer connected this go around.

[Alvin]

It will reset often. several times in 10 minutes sound right.. Sounds like it is riding a LTIT and STIT error. A log would tell me more.

[2xLS1]

Well the IAC counts shouldn't be at 0 See if you can get them up a little. Is the blade cracked open too much with the screw or the hole in the blade too big? That could be causing it.

[RDF1]

Ill have to get a charger for my tooning laptop tomorrow. Im having issues with my old one

But yes seeing the idle trims and such so far out makes since.

Earlier i closed the TB as far as i could and the blade is sticking in the bore now. IAC is still low.
Smoked tested it again and finding nothing. Even Taped the TB opening to try and help smoke show a leaker.

Measured the hole in the TB Blade and its very close to the other ones i have in the shop. Within a couple thousandths using pin gauges.

Its got a decent size cam in the 5.3 and id expect the TB Blade to need to be opened more to meet the 850rpm idle and IAC to be in the 50s atleast.

[RDF1]

I also disconnected and plugged the vac hose to the brake booster with no change. The valve cover is new with the updated pcv.

[Alvin]

Use the scanner to purposefully drive the IAC around. Make sure the idle responds. There is no feedback on IAC.. Its basically told to run into a stop on startup.. then count back x steps. It's keeping count of where it was driven too but no feedback on if it actually made it.