NOTE: The following test is for models with separate Idle Speed Control only. For models with integral fuel injection and idle speed control systems, see FUEL INJ - BOSCH LH article in the FUEL SYSTEMS section.

Locate ECU at right kick panel. Unplug both ECU harness connectors. Turn ignition on. Ensure 12 volts are present at terminal No. 1. Ensure terminal No. 2 has continuity to ground.
Connect a tachometer between terminal No. 12 and ground. Start engine. Tachometer should indicate engine RPM.
Some models with A/C have a White/Green or Red wire attached to terminal No. 7. If so, turn A/C on and ensure there are 12 volts present at terminal No. 7.
NOTE: During A/C operation, the engine speed should increase about 150 RPM.
Using jumper wires, connect one jumper wire between terminals No. 1 and 4. Connect another jumper wire between terminals No. 2 and 5. Start engine. If engine speed increases to 1600-2400 RPM, the ACV is okay. If not, check wiring and ACV.
Repair or replace any defective components or circuits. Remove jumper wires. Connect all harness connectors. Check to see if idle speed control system is working. If not, ensure all connectors are clean and tight. If no problems are found, but idle speed control system is still working incorrectly, replace the ECU.

When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

• You smell fuel, burning insulation, or see smoke.

• Brakes feel soft, pull hard to one side, or make grinding noises.

• The engine overheats, stalls repeatedly, or misfires under load.

• You are missing required tools, torque specs, or safe lifting equipment.

• You are not confident in the next step or safety outcome.

Safety Warning

Ecu Circuit Tests

Use the Manual With the Right Hardware

When to See a Mechanic