IAC and TPS Setting Procedures
IAC valve setting procedure:
The ECM controls idle rpm with the IAC (idle air control) valve. The idle rpm is programmed into the PROM. To increase idle rpm the ECM moves the IAC valve out allowing more air to pass by the throttle plate. To decrease rpm it moves the IAC valve in to reduce air past the throttle plate. A scan tool will read the ECM commands to the IAC valve in counts. Higher the counts the more the air is being allowed to pass the throttle plate (higher idle). Lower the counts the less the air is being allowed to pass the throttle plate (lower idle).
The TPS (throttle position sensor) provides the ECM a voltage signal that changes relative to the throttle blade angle. The TPS signal is one of the most important inputs used by the ECM for fuel control and for most of the ECM control outputs. The signal voltage will vary from about .4 at idle to about 5 volts at WOT (wide open throttle). A TPS signal reading less than 0.20 volts while the engine is running will set a trouble code 22. A TPS signal reading more than 4.90 volts while the engine is running will set a trouble code 21. A TPS idle setting above .47 could result in drivability problems.
(Note: To connect a voltmeter take a sewing pin and probe the middle red wire. Connect voltmeter positive lead. Take another sewing pin and probe the bottom black wire. Connect voltmeter negative lead.)
* If the idle and WOT settings are within range go to step 10.
(Note: Any obstruction under the accelerator pedal such as a floor mat and transmission TV dent cable adjustment can affect WOT TPS setting. It�s best checked by a friend pressing down on the accelerator pedal.)
Joe Lubrant's IAC Setting Procedure:
Put ECM into Diagnostic Mode (jumper the top far right 2 ALDL connector pins) with key on-no start. Disconnect the IAC plug, then turn off key, remove ECM from diagnostic mode (remove ALDL jumper), start engine with scan tool attached, set idle to 650 to 680rpm. When completed shut off engine reconnect IAC plug. Turn key back on and reset TPS to .4v to .42v closed and approx. 4.6v to 4.65v WOT. Then clear ECM by disconnecting the orange wire by battery for a few seconds and reconnect. (finished)
I don't use IAC numbers as a general rule because of some variables with the types of throttle bodies out there. Some of the machining fit on throttle bores & plate sizes leave a little to be desired, and in cases effect by-pass air #s.
The 650 to 680rpm IAC setting is approx 100 rpm below the commanded chip program, and also becomes part of the stall saver.
90% of tip-in or off idle stumbles are mis-adjusted IAC's, the others are normally bad MAF's or air leaks.
TurboDave's IAC Setting Procedure:
Or you can use my tried and true method, all it requires is a scan tool that monitors IAC, and you have one. That method you tried is incredibly old, terribly out of date and designed strictly to get you "somewhere in the ballpark" if you don't have any scan tool to use at all. It's an old old old Buick mechanics method. Just get your scan tool up and running and keep an eye on IAC numbers and idle TPS values. Now start adjusting the Minimum Air Bleed Screw on top of the throttle body to start bringing the IAC's down. Do this by turning the screw CW. You'll notice with each quarter turn the rpm will momentarily increase, but the chip will bring the rpm right back to normal. It does this buy decreasing the IAC's. About each half turn, you should re tweak the TPS idle setting to keep it close. Then when you get the IAC's down anywhere in the 10-20 range in park/neutral, you can give the TPS it's final tweak. You'll be amazed at the simplicity and ease. No guesswork involved. That old method you've been trying is a very very old Buick mechanics way of "ballparking" his best guess, in the absence of scan tools. And as many many GN guys are finding out, it just doesn't work most of the time. With the modern equipment we have available there's no reason to use that method. Use the tools at hand and do it right the first time.