General Motors — Idle Air Control Functional Test
Testing & diagnosis · Electronic Throttle Body / TAC Motor
From a General Motors service manual — check it applies to your exact model before use.
Procedure
- Engine should be at normal operating temperature
- Start engine, allow idle to stabilize and record RPM
- Ignition OFF for 10 seconds, disconnect Electronic Throttle Body harness connector
- Restart engine and record RPM; RPM should be higher by more than 200 RPM
- Reinstall connector; idle speed should return within 75 RPM of original within 30 seconds
- If not, with ignition OFF for 10 seconds disconnect the throttle body harness connector and restart the engine
- Using a test lamp J 34142-B connected to ground, probe each one of the six Electronic Throttle Body harness terminals
- Locate and repair poor connection, open, or short to ground in the circuit that did not blink
- Check for poor Electronic Throttle Body connections or replace the faulty Electronic Throttle Body
- Repair faulty ECM connections or replace faulty ECM
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Idle RPM differential: 200 RPM
- Idle return tolerance: 75 RPM within 30 seconds
Source: General Motors service manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.