I just replaced my IAC about 2 to 3 months ago due to a high RPM issue. That did help it one bit. Its an 88 IROC, 5.7 with 65 thousands miles. The car will idle in park at just over 1000 and in drive at about 7 to 800. I just tried resetting it using the tech article and my torx screw is as far back as it goes and no change in idle. In fact the second I turned it back it stopped touching the throttle cable connector. I dont know what to do anymore except probably taking it somewhere to the ECM scanned. Anyone have any last chance ideas before I resort to this?

 

Thats normal for these cars. on start up(Park) it will idle at 1000 until the car warms up , Once warm it will come down to normal RPM.... in drive you should be seeing 650RPM ...Try going thru the procedure again..thats strange it should be touching the throttle connector........Make sure you put the car in drive not park when resetting the AIC....Put blocks on all 4 tires...dont want you ride running away on you ......Adjust your TPS after the AIC...Set the TPS to .54V.....Your TPS will be off due to the AIC adjustment...

 

The problem with the IAC reset I did was when I adjust the torx screw back it no longer is touching the throttle setup. Its as far back as it is allowed to go. Even when my car warms up it still idles just as high. Living in Florida it doesnt take long to warm up anyway.

 

You checked and made sure there are not any vacuum leaks, correct? If you unscrewed the torx bit until it is not touching the throttle body blade bracket and it is still idling high, then you probably have a vacuum leak somewhere.

 

Havent found a single vacuum leak either.

 

y put it in drive for resetting the iac?

 

You put it in drive just to double check the ide RPM under slight load. It will be less than the RPM in neutral. So you know what it will be like when driving and coming to a stop.

 

ok i set mine in park is that ok?

 

That's fine, but the idle RPM spec listed on the underhood emissions tag is in drive. If it idles how you like it then leave it.
I just reset the idle on my friends Z28 and the tach doesn't work on that car. I didn't have my scanner hooked up, so I just set it by ear. I forgot to double check what it actually is.

 

Factory tach isn't necessarily the most accurate piece of electronics in the world. I double-check them against what the ECM reports to see how far off it might be. 100-150 RPMs difference is very common in my experience, while others are WAY out to lunch. I trust what the ECM reports much more than what the tach indicates.

When setting the IAC, there's really not much to it except getting the miminum idle speed set right. I forget the exact procedure, but it's something like:

warm up engine
hold engine speed over 2500 RPMs for 2 minutes
unplug IAC WHILE STILL HOLDING ENGINE RPMS OVER 2500 RPMs.
When you let off the gas the idle will drop to the minimum idle speed (IAC should be fully closed). Set this idle speed to spec (500 RPMs?? Somewhere a little below normal idle speed in any case)
Shut off
Reconnect IAC, ECM will regulate idle speed from there as normal (or should, if things are working right)

Main thing is, when you do the minimum idle speed procedure you SHOULD be able to get it to idle down below normal ECM-adjusted idle speed. If so, then the IAC is working right and is holding that higher idle speed as it should under ECM command. If not, then you've got mechanical and/or vacuum leak issues.

And, before I forget, don't overlook simple stuff like the throttle cable not allowing the throttle arm to return fully to the curb idle screw!

 

Also it is 1 1/8" from the tip of the IAC to the bore gasket, when fully extended. I would also check the IAC steps to see if they are near the 20 counts or less at idle speed. High steps = high speed. Vacuum leaks in the throttle bores are common in higher mileage engines.

 

but how can u tell the step counts?

 

IMO, anyone that owns one of these cars should have something like this:
http://www.moates.net/product_info.p...roducts_id=127
I've been using TunerPro for the PC software, but there are other programs available.

 

You are overcomplicating the issue. IAC control is a constantly active PID loop. Take away the feedback or an input, and the loop goes out of control. Forget about all this conjecture, rumor, half-truths, and misinformation. Read the factory service manual.

Set the throttle minimum air position with the engine at full operating temperature, all accessories (including fans) off, IAC fully closed and disconnected, auto trans in DRIVE.

IMPORTANT! The IAC counts don't actually mean F'KIN THING! When you finally accept that fact, you might actually be able to accomplish something. I've watched IAC counts bounce all over the place on my MT2500 under various conditions.

The reported IAC counts only indicate the number of steps that the ECM thinks it is sending to the IAC stepper motor. If the IAC is not responding and complying 100%, it doesn't really indicate IAC pintle position at all. You need to verify (not using IAC counts) that the IAC pintle is fully closed and not leaking any air past the throttle plates. Once that is done, set the throttle stop screw to the specification. Period. If there is a problem with idle control after that, the problem is NOT in the throttle minimum position.

(I must have typed this three hundred times here in the last eight years.)

When you get the TB minimum air set, the rest is up to the IAC. If you cannot get the TB minimum air set, there is a leak - Period.

 

To further illustrate this point, I just reset the idle on the 91Z I'm working on. It was idling way too high, and the throttle screw was completely backed off. When I scanned it, the IAC counts were only around 40. When I actually pulled the IAC housing off the throttle body to see where it was, it wasn't fully extended. I ended up pulling it out, taking it apart, cleaning it, putting it back together, setting the length. Then while still leaving the IAC housing off the throttle body I did the first part of the reset to make sure it was fully extended and the pintle was sealing off. I also had to clean up the plug as it wasn't making a good connection.
Put it all back together and finished setting it. Idles great now.
As for setting it in drive, since I was doing it myself with no help what I was doing is tweaking the idle stop screw while in park, and then going back putting it in drive and seeing how it idled, then back in park and adjusting as needed.

Bobby since you live in CT if you want I can give you a hand with it.

 

Vader

Quote: "IMPORTANT! The IAC counts don't actually mean......"

(I must have typed this three hundred times here in the last eight years.)


Did you ever get the feeling that you were teaching a class, in which the students are constantly changing, new ones every post. So everyday is the first day of school? (something like the movies "Ground Hog Day" or "50 First Dates")

To relieve typing stress, make a copy of an often repeated answer (sticky?), then cut and paste to the repeated posts, for the people who are "search challenged".

Quote:"The reported IAC counts only indicate the number of steps that the ECM thinks it is sending to the IAC stepper motor."

Stepper motors are a game of "Blind Man's Bluff". The Ecm sends out "X" number of pulses/counts and assumes that "all orders are carried out".

What the ECM looks for is, what the programed IAC PID loop wants, like idle speed. Speed under target idle speed (channel/hole plugged up) more pulses, Speed over target idle speed (vacuum leak) less pulses.

I have seen the pulses/counts just run continuously (to some max/min value), when the needed condition was not obtained (like idle speed).

The ECM does not know or care, if the wires are hooked up, the stepper motor has open/shorted windings, the pintle is stuck, the hole is plugged, the pintle length is calibrated, or anything else.

There is no stepper motor feedback. High dollar circuits have pulse coders on the output shaft of the motors, and count the pulses out vs pulses in, to show proper movement of the shaft.