Idle Speed/Throttle Actuator - Electronic: Testing and Inspection

Motronic ECU Harness Connector (pin # Locations):

It is not necessary to test the idle stabilizer valve unless the idle speed is incorrect or a fault code has directed you to this test procedure. If idle speed is incorrect, before testing idle stabilizer valve make sure there are no vacuum leaks or crankcase leaks where engine vapors and air can be exchanged. Also check the ignition distributor basic adjustment.

1. Disconnect idle stabilizer valve and install parallel test leads between valve and its harness connector so that the dwell can be read while valve is operating.

2. Connect dwell meter to test leads and start engine. Set dwell meter to 4 cyl. scale.

^ With engine idling at normal operating temperature and no load (electrical or other), typical dwell reading is 30~ (this may vary slightly depending on the particular software in the ECU, and other conditions such as engine wear, air flow sensor adjustment, minor vacuum leaks, etc.) If there is no dwell reading, check for:

a. Battery power at idle stabilizer valve electrical connector terminal #2 (Blu/Blk wire). Should have battery power when the ignition is turned on. If not, check for open circuit between connector terminal #2 and fuse #28 in fuse relay panel.
b. Open or grounded circuit between idle stabilizer valve connector terminal #1 (G/Blk wire) and ECU terminal #17.

If no wiring problems are found and there is still no duty cycle signal from ECU, then ECU is faulty. If there is a dwell reading, continue testing.

3. Open throttle slightly so that engine speed increases to approx. 1,000 rpm and idle switch is open. Note dwell.

^ Dwell should increase slightly from previous reading.

4. Let engine idle again. After a few seconds, note idle stabilizer dwell.

5. Create a load on the engine by placing the transmission in a drive gear (automatic trans) or turning on an electrical load such as the fresh air fan, headlamps, window motor, etc. Note dwell change.

^ Dwell should increase and engine speed should remain relatively constant.

6. Turn on the A/C, and note engine speed and idle stabilizer dwell.

^ Engine speed should increase slightly and idle stabilizer dwell should increase significantly (more than in previous checks).

If idle stabilizer dwell responds as described, but engine idle speed is not maintained (or increased in step 6), then replace idle stabilizer valve. If dwell does not respond, check all related components and wiring. If wiring is OK and dwell still does not respond as described in this test procedure, then ECU is faulty.