So ive been having this reoccuring issue with my IAC, Ive run a datalog of it and for the life of me i cannot figure out how to fix the issue.

On the mechanical/visual side of the house: my idle has been higher than usual, tach is reading 2k at idle when in reality its only 1550 according to the ecm. I attempted my IAC cleaning and minimum air reset which ive done plenty of times before. Didnt help at all. The car will idle fine RIGHT after the reset (first start) then when i shut the car off and start it again the idle goes right back up and does all the time from start. I was hoping someone could look at the datalog for me and give me a heads up, ive stumped the local thirdgen owners.

I did not change anything when this problem occured, i just got in my car and started it and the idle was high. So i cleaned the IAC and reset minimum air, no help. Ended up snapping the IAC on accident because i was being clumsy, so i bought a new one to replace it. minimum air reset and no luck. Broke out the laptop and saw my TPS was acting lazy, got a new one.....no luck. Its dialed in at .54 volts, the CTS is reading accurately and im confused at this point. Ive even swapped ECMs with a known good TBI ecm with a custom prom.... no change in my minimum idle. My throttle plates are pretty much closed, no excessive opening on the blades. No shaft play from worn bushings (rebuilt TBI in 09) This car has been my daily driver for 5 years now and ive never seen this issue, could someone take a look at my datalog and see if they spot anything weird? Im far from a pro with this, kind of on a learning curve at this point.

Any help would be greatly appreciated

 

It is getting the air from somewhere? Doing the reset solves it temporarily....When you drive the car over 40 mph I believe the ECU does something to it like in a learn.
I presume you did not see issue after purchasing a IAC? There are several that GM uses for shape of pindle.

Can you do a visual while car is idleing to see the pindle position? I suspect it is clearly out of position. If it appears in position I would temporarily plug the passageway to see if idle decreases significantly. If so it is not seatuing far enough.

Do you run a IAT? I wonder if the signal is eroneous showing cold incoming. Not sure if it only compensates for A/F. Coolant sensors usually fail showing cold when in fact hot.

 

I posted the video in my tbi thread, the pintle sits half way closed, computer reads 50 steps, can't lower it from there, the CTS is showing a number on the datalog but its at the bottom of the graph no line for it, temp is on point with my gauge no cold when hot, I was told to move the throttle screw without grounding the aldl which should effect the steps, when I opened the plates more steps increased and when I backed it out they wouldn't drop below 50, I was told to aim for around 15 so I'm wayyyy off at this point. No vacuum leaks present just the iac creating a leak

 

I will say 50 steps is about 25% open. If it is actually half way or 50% visually it is then a IAC defect or the ECU is sending a wrong signal. Unlikely the ECU is defective. Either way it is open too far. I think GM has is set 10-25 steps. I have the stock LO3.bin at myt residence. I could take a look.

Did you ever manually adjust the pindle? I dont believe it is something you do upon install of a new one.

 

I've never manually adjusted any pintle, I just run it down so it won't jam into the passage and do the minimum air reset, I know the ecu isnt to blame because I swapped it for a known good one and there was no change, the pintle moves fully upon shutting down, I replaced the iac with a new one when my old one started acting up, high idle and such so I cleaned it and it didn't change, I don't think the chances of getting a bad iac are too high but it is a possibility, when I tweaked the idle screw the steps didn't lower but the idle did and it stays consistant now, steps are just still high

 

Moving the idle screw will move the steps due to commanded idle speed but the steps you see in datalog are where the IAC pindle should be not where they are. When I first wired the IAC it was miswired however the steps looked good in datalog and they were not where log said they are.

 

I would take it back to store and suggest it is defective and try another one. I presume the TB is stock for yr make model.