Testing Idle Air Control (Iac) Motor; Testing Coolant Temperature Sensor; Testing Air Charge Temperature Sensor; Testing The Oxygen Sensor - Holley MPI PRO-JECTION Installation Tuning And Troubleshooting Manual

Fuel injection system

Table of Contents

18.4 Testing Idle Air Control (IAC) Motor

A simple test for the IAC motor is as follows:

1 - Remove the air cleaner assembly. Check the electrical connections at the IAC motor and at the ECU for integrity.

2 - With the warm engine idling in neutral, place your finger slowly over the IAC opening. The idle speed should drop and the

suction on your finger will increase.

3 - After 5 or 10 seconds, remove your finger from the opening. The engine idle speed should increase and then slowly

return to normal.

4 - If your engine speed does not respond as described, the IAC motor is defective and must be replaced.

DANGER!

ROTATING OR HOT PARTS IN AN ENGINE COMPARTMENT CAN CAUSE BURNS, SERIOUS INJURY

AND/OR DEATH IF CONTACTED WITH A PERSON. KEEP LOOSE CLOTHING AND BODY PARTS AWAY

FROM ROTATING OR HOT PARTS.

1 - Remove the coolant temperature sensor from the manifold. Allow the sensor to reach room temperature, approximately

70° F.

2 - With a digital voltmeter set to measure resistance and connected to the pins of the coolant temperature sensor, the

resistance should read approximately 3,800 Ω.

3 - Place the sensor in boiling water with the voltmeter leads still connected. The resistance with the water boiling (212 F)

should be approximately 182 Ω.

4 - If your coolant temperature sensor does not respond as described above, the sensor is defective and must be replaced.

1 - Connect a digital voltmeter set to read resistance to the air charge temperature sensor leads and not the resistance value.

2 - Using a hair dryer, warm the tip of the air charge temperature sensor. The resistance should decrease as the tip is

heated.

3 - If your air charge temperature sensor does not respond as described above, the sensor is defective and must be replaced.

The MPI PRO-JECTION systems oxygen sensor performance can be evaluated. The oxygen sensor voltage can be checked

through the monitor option of the MPI PRO-JECTION software. The other option if no PC is available is to probe the gray wire

from the oxygen sensor connector with the positive (+) lead of a digital voltmeter. With the engine running open-loop, the meter

reading should be near zero or one volt. During closed-loop operation, the readings should constantly change between zero and

one volt. If the reading is always zero volts, be sure +12V and ground are present on the YELLOW and BLACK wires. If so, the

sensor is probably bad. If you see a changing voltage, but the readings do not vary far from 0.5 volts, the sensor is lazy and

should be replaced.

WARNING!

Be sure to use a high impedance digital voltmeter. An older style analog (dial type readout) has an

internal resistance that is too low and will destroy the oxygen sensor if connected to the gray wire.

Table of Contents