Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the IAC valve.
- Connect the J 37027-A to the IAC valve. See Special Tools .
- Engine running, command the IAC valve in until 600 RPM is reached with the J 37027-A
, then command the IAC valve out until 1,800 RPM is reached then lower the idle to 800 RPM. See Special Tools . The engine speed should steadily increase and decrease as commanded.
- If the idle does not increase or decrease steadily, verify one of the following conditions is not present:
- A clogged IAC passage
- Excessive deposits on the throttle plate or bore
- Excessive deposits on IAC valve pintle or bore
- Restricted air intake system
- The throttle body for damage and/or tampering
- Vacuum leaks
- Malfunctioning PCV valve
- If all conditions test normal, test or replace the IAC valve.
- If the idle does not increase or decrease steadily, verify one of the following conditions is not present:
- Engine running, command the IAC valve out until 1,800 RPM is reached then lower the idle to 800 RPM with the J 37027-A
. See Special Tools . The test lamp should flash.
- IAC A High Control terminal D
- IAC A Low Control terminal C
- IAC B High Control terminal B
- IAC B Low Control terminal A
- If the test lamp does not illuminate, test the applicable control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- If the test lamp does illuminate, but does not flash, test the applicable control circuit for a short to voltage. If the circuit tests normal, replace the ECM.
- If test lamp illuminates and flashes, test the applicable control circuit for high resistance. If the circuit tests normal, replace the ECM.
- If all circuits test normal, test or replace the IAC valve.
IMPORTANT:
This test must be performed on all of the IAC control circuits.