When the CHECK ENGINE warning light has been reported on, turn the ignition on, move the driver's seat to the front position and observe the LED on the rear of the Electronic Control Unit (ECU). The LED indicates a system failure by it's blinking frequency.

If the ECU indicates codes 4, 11, 15, 16, or exceeds 17, count the blinks again. If the indicator is blinking these codes, substitute a known-good ECU and recheck. If the indication goes away, replace the original ECU.

The CHECK ENGINE warning light and ECU LED may come on, indicating a system failure, when in fact, there is a poor or intermittent connection. First, check the electrical connections, clean or repair connections if necessary.

Fast Idle Testing:

Testing and Inspection


NOTE: Do not attempt to disassemble the Fast Idle Valve, it is factory adjusted.



Start the engine.
Remove the cover of the fast idle valve.



Put your finger on the valve seat area and make sure that there is air flow with the engine cold (coolant temperature below 86°F, 30°C) and idling.
If there is no air flow, replace the Fast Idle Valve and retest.
Warm up the engine to normal operating temperature (the cooling fan comes on).
Check that the valve is completely closed (no air suction can be felt in the valve seat area).
If any suction is felt, the valve is leaking. Replace the Fast Idle Valve and recheck.





The Fast Idle Valve, mounted on the throttle body next to the throttle angle (TPS) sensor, raises the idle speed when the engine is cold. The Fast Idle Valve is controlled by a thermowax plunger type valve. When the engine coolant is cold, the thermowax contracts the plunger allowing air to bypass the throttle plate and idle adjusting screw into the intake manifold. When the engine coolant warms up, the valve closes and the bypass air flow is blocked.