The base engine idle adjustment procedure (minimum air rate) is recommended annually or when modifications such as installing a different chip are done. The minimum air rate adjustment is essentially calibrating the true base engine idle RPMs in correlation with the electronics and TPS zero percent throttle perimeters. Before beginning this procedure, the throttle body and IAC seat and motor pintle MUST be free of carbon deposits and thoroughly cleaned to enhance proper airflow, this is commonly done with carburetor cleaner and a rag. The following instructions will assume a scan tool is being used to access ECM data.
1) Warm up engine to operating temperature, then shut it off.
2) Put ECM in diagnostic mode and turn the ignition to the run position, diagnostic mode can be confirmed with the check engine light flashing code 12.
3) Wait 45 seconds, and then disconnect the IAC motor 4-pin connector.
4) Put scan tool in open mode (road test) and start engine.
5) Confirm closed loop status.
6) Put Emergency brake on and or block tires and put shift lever in "DRIVE".
7) Using the throttle blade adjustment screw on the throttle body, set the idle speed to 500 RPM +- 50 using only the scan tool RPM display.
8) Put shift lever back in the PARK position.
9) While the engine is still running, adjust the TPS to .046. If your TPS was well above or below this setting, it might be a good idea to recheck step #7 once more.
NOTE: It's suggested the idle TPS setting be done while charging system is operating.
10) Turn the engine off and reconnect the IAC wire connector,
turn key back on to the run position and set maximum TPS value
to at least 4.7 volts with throttle blade at WOT, recheck step
9 and 10 back and forth till both settings are obtained.
NOTE: To obtain 4.7 volts at WOT, it may be necessary to remove the TPS and trim off enough material from the banana shaped tabs to allow the sensor to shift closer to the front of the vehicle, this shifting will move the TPS throw arm closer to the throttle shaft throw pin changing the fulcrum point increasing TPS voltage output.
11) It is now necessary to clear the ECM memory. Disconnect
the ECM power supply and wait at least 10 seconds then reconnect.
12) Test drive car and sustain 45 MPH for 300 yards, the ECM will now command an IAC reset and update its counts so the ECM will now know where the IAC is in relation to its seated position.
Text (c) John Pearcy