Check your IAC
Idle Air Control (IAC) Valve
The IAC valve, mounted on the throttle body, controls idle speed by regulating throttle plate by-pass air. IAC valve includes an air by-pass valve and idle speed control solenoid valve. The air by-pass valve is affected by the engine coolant temperature and functions during cold engine conditions less than 122 F (50 C). The idle speed control solenoid is controlled by PCM and works throughout the entire temperature range.
On some models, idle is controlled by idle speed control air by-pass valve. A throttle air by-pass valve is a solenoid-operated valve controlled by PCM. The valve allows air to by-pass throttle plates to control cold engine fast idle, no-touch start, dashpot, overtemperature idle boost and engine load idle correction.
Air by-pass channel carries idle airflow regulated by air by-pass valve. Air by-pass valve is controlled by PCM to adjust both cold and warm idle speeds. Air by-pass valve uses solenoid valve to vary idle airflow volume allowed to enter engine.
4) Measure IAC Solenoid Resistance
Turn ignition off. Disconnect IAC solenoid. Connect DVOM positive lead to VPWR terminal and negative lead to IAC terminal. See Fig. 53 . Measure resistance of IAC solenoid. If resistance is not 6-13 ohms, replace IAC solenoid and repeat QUICK TEST. If resistance is 6-13 ohms, go to next step.
Fig. 53: IAC Solenoid Connector (KE2)
5) Check For Internal Short To IAC Solenoid Case
Turn ignition off. With IAC solenoid disconnected, measure resistance from either IAC terminal pin to IAC solenoid housing. If reading is more than 10,000 ohms, go to next step. If reading is 10,000 ohms or less, replace IAC solenoid. Repeat QUICK TEST .
6) Check VPWR Circuit Voltage
Leave IAC harness disconnected. Turn ignition on. Measure voltage between VPWR terminal at IAC harness connector and battery ground terminal. If voltage is 10.5 volts or more, go to next step. If voltage is less than 10.5 volts, repair open in circuit and repeat QUICK TEST.
7) Check IAC Circuit Continuity
Turn ignition off. Leave IAC solenoid disconnected. Disconnect 60-pin PCM connector. Inspect terminals, and repair if damaged. Install EEC-IV Breakout Box (T83L-50-EEC-IV), leaving PCM disconnected. Measure resistance between test pin No. 21 and IAC terminal at IAC wiring harness connector. If reading is 5 ohms or less, go to next step. If reading is more than 5 ohms, repair open circuit and repeat QUICK TEST.
8) Check IAC Circuit For Short To Ground
Turn ignition off. Leave IAC solenoid and PCM disconnected. Measure resistance between test pin No. 21 and test pins No. 40, 46 and 60. If any reading is less than 10,000 ohms, repair short to ground and repeat QUICK TEST . If all readings are 10,000 ohms or more, go to next step.
9) Check IAC Circuit For Short To Power
Leave IAC solenoid and PCM disconnected. Turn ignition on. Measure voltage between breakout box test pin No. 21 and chassis ground. If voltage is more than one volt, repair short circuit and repeat QUICK TEST. If code or symptom is still present, replace PCM. If voltage is one volt or less, go to next step.
10) Check IAC Signal From PCM
Turn ignition off. Reconnect IAC solenoid. Connect PCM to breakout box. Connect DVOM between test pins No. 21 and 40 at breakout box. Start engine. Observe DVOM while slowly increasing engine speed to 3000 RPM. If DVOM voltage reading is 3.0-11.5 volts, go to next step. If DVOM voltage reading is not 3.0-11.5 volts, remove IAC solenoid to confirm that it is not stuck open. If IAC is okay, replace PCM and repeat QUICK TEST.
11) Check Base Idle
Verify base idle speed is correct. See ADJUSTMENTS article in this section. If base idle speed is within specification, remove IAC solenoid and inspect for contamination. Repair or replace as necessary. Repeat QUICK TEST. If code or symptom is still present, replace IAC solenoid. If base idle speed is not correct, reset idle speed to specification. Repeat QUICK TEST . If unable to set idle to specification, go to next step.
12) Check For Faults Affecting Idle Speed
Check following mechanical items for faults:
Throttle linkage and/or cruise control linkage (sticking or binding).
Throttle body (contamination).
Vacuum hoses. Check Vehicle Emission Control Information VECI) label.
Check for leaks around IAC solenoid (gaskets, etc.).
If any of these items are faulty, service as necessary, and repeat QUICK TEST. If all of these items are okay, remove IAC solenoid and inspect for contamination. Repair or replace as necessary. Repeat QUICK TEST. If code or symptom is still present, replace IAC solenoid. Repeat QUICK TEST.
NOTE:A break in step numbering sequence occurs at this point. Procedure skips from step 12) to step 15). No test procedures have been omitted.
Saturday, November 29th, 2008 AT 9:19 PM