IAC Diagnostic Service Tips - General
Never clean an IAC valve. Carburetor cleaners and other cleaning agents may temporarily repair the drivability concern, but the long-term functionality of the valve is compromised.For all drivability concerns, make certain the service writer obtains as much information as possible from the customer as to the conditions causing drivability concern. Attached is a drivability concern check off sheet (Figure 2) that if used, can help reduce the time required to diagnose a vehicle.
NOTE
IF THE ENGINE STALLED WHILE THE VEHICLE WAS IN GEAR AND MOVING THE POSSIBILITY OF THE IAC VALVE CAUSING THIS IS UNLIKELY UNLESS IT OCCURRED ON DECELERATION.
Use the following Supplemental information for 3.0L 4V Duratec Engines, in the Taurus/Sable, and Lincoln LS.
1. Use the following conditions for the test described below:
^ Transmission in park
^ Engine temperature should be at least 190° F
(88°C)
^ All accessories should be off steering wheel in the center position
^ EGVR and EVAPDUTY CYCLE at zero, if the vehicle has an EGR system
^ Short and long term fuel trims less than 15%
^ At stabilized engine speed (RPM) and temperature (hot idle) per the Powertrain Control Emission Diagnostics (PC/ED) manual, verify the IAC duty cycle is within reference values called out in the chart in this TSB.
NOTE
IT IS USUAL TO SEE THE IAC DUTY CYCLE VARY BY 1% TO 2% OVER SEVERAL MINUTES.
If the Duty Cycle is out of specification, proceed with the following steps:
1. Ensure that there is no purge flow.
2. Verify PCM harness integrity by performing a wiggle test on the harness while the engine is running and observe the IAC duty cycle and engine performance. Should abnormalities be observed, repair the harness as required.
3. For an IAC duty cycle high concern, unplug and plug in the IAC power connector several times. If the duty cycle remains high, replace IAC valve.
4. For an IAC duty cycle low concern, there may be an intake air leak. See the below IAC diagnostic service tip for DTC 1506 and other high idle concerns.
Use the following Supplemental Information for the 3.9L Lincoln LS and Thunderbird.
1. Use the following conditions for the test described below:
^ Transmission in park
^ Engine idle at approximately 650 RPM
^ Engine temperature should be at least 190° F
(88° C)
^ All accessories and the engine cooling fan should be off
^ Steering wheel in the center position
^ EGRVR and EVAPDUTY CYCLE are zero
^ Short and long term fuel trims less than 15%
NOTE
IT IS USUAL TO SEE THE IAC DUTY CYCLE VARY BY 1% TO 2% OVER SEVERAL MINUTES.
NOTE
IT IS EXTREMELY IMPORTANT TO CHECK THE IAC DUTY CYCLE WHEN THE RPM IS AT 650 RPM. EVEN 700 RPM IS TOO HIGH FOR CHECKING the IAC VALVE DUTY CYCLE UNDER THESE CONDITIONS. IF THE RPM IS OVER 650 RPM, MOMENTARILY OPENING AND CLOSING THE THROTTLE AND A SHORT EQUILIBRATION TIME WILL LOWER THE RPM.
At stabilized engine speed and temperature, verify that the IAC duty cycle is between 27-36% with no purge flow (EVAPV duty cycle is 0%).
If the Duty Cycle is out of specification, proceed with the following steps:
1. Ensure there is no purge flow.
2. Verify PCM harness integrity by performing a wiggle test on the harness while the engine is running and observe the IAC duty cycle and engine performance. Should abnormalities be observed, repair the harness as required.
3. For an IAC duty cycle high concern, unplug and plug in the IAC power connector several times. If the duty cycle remains high, replace IAC valve.
4. For an IAC duty cycle low concern, there may be an intake air leak. See the below IAC diagnostic service tip for DTC 1506 and other high idle concerns.
NOTE
IF THE ORIGINAL IAC VALVE WAS WITHIN DUTY CYCLE SPECIFICATION OR THE DUTY CYCLE REMAINS OUT OF SPECIFICATIONS AFTER IAC VALVE REPLACEMENT FURTHER DIAGNOSTICS ARE REQUIRED TO ADDRESS THE CUSTOMER CONCERN.
Use the following Supplemental Information for 4.0L SOHC Engines In the Ranger, Explorer, Mountaineer, Explorer Sport and Explorer Sport Trac.
If no DTC's present check the following items in this order before examining the IAC valve:
^ BARO Hz reading - Refer to Barometric Pressure Chart listed in this TSB
^ Battery and fuse box power lead
^ Ground wire attachments
^ Wiring (wiggle test)
^ PCM voltage
^ Vacuum leaks
Examine AC valve under these conditions:
^ PCM updated to the latest available calibration
^ Transmission in park
^ Warm stabilized vehicle with engine temperature at least 190° F (88° C)
^ All accessories and cooling fan sh6uld be off
^ Steering wheel in the center position
^ EGVR and EVAPDC at zero, if the vehicle has an EGR system
^ Short and long term fuel trims (less than 15)
Perform the following steps in order:
1. Using either NGS or WDS bring up the following PIDS: IACTRIM, IACKAM2, IACKAM3.
2. Allow vehicle to idle until the IACTRIM PID is 0.
NOTE
IACTRIM ALWAYS TRIES TO GO TO 0. WHEN MOVING TOWARDS 0, THE IACKAM2 PID SHOULD BE CHANGING. IF IACKAM3 IS CHANGING, THEN THE AIR CONDITIONING SHOULD BE TURNED OFF.
3. If IACKAM2 is between -0.35 and +0.35 with IACTRIM=0, then the valve is operating properly at idle. The remainder of this TSB will help diagnose true root cause.
4. If IACKAM2 is not between -0.35 and +0.35, it is highly likely that the engine idle system (to include the throttle body and air intake system) -is not operating properly.
NOTE
FOR ALL VEHICLES PLEASE RECORD THE OBSERVED IAC DUTY CYCLE AND ENGINE RPM IN THE WARRANTY CLAIMS COMMENTS FOR THIS DIAGNOSTIC.
IAC Diagnostic Service Tips - DTC 1506 (IAC Over Speed Error) and other High Idle Concerns:
^ There are two primary causes of high idle:
1. Damaged IAC valves and
2. Vacuum leaks
^ AC valves can be damaged from engine induction backfires. Many times the customer may not notice the induction backfire but will notice the high idle afterwards. Indications of valve damage can be a shiny, almost polished appearance in the interior of the valve and a dislocated pintle. An IAC valve damaged by backfire should be replaced. Refer to Figure 1.
^ Inspect PCV system for leaks especially looking for cracks along any rubber elbow joints; also verify that the correct PCV valve is installed.
^ Inspect for vacuum hoses loose or disconnected from intended ports and connections. Induction backfire can loosen or disconnect vacuum hoses.
^ Two indicators can help you identify if a vacuum leak is present, even if the engine RPM appear normal in the service bay. If the duty cycle is below specification that is indicative that the engine is receiving too much air (from a vacuum leak) and the PCM is ordering the valve to close up to restrict flow. Another indication is fuel trim. Record the long term and short term fuel trim PIDS (LONGFT1, LONGFT2, SHORTFT1, etc.), if short term fuel trims are high (above specification) this is a possible indication of a vacuum leak, making the engine run lean, and the PCM is attempting to compensate.
IAC Diagnostic Service Tips - DTC 1507 (IAC Under Speed Error) and Other Low Idle
Concerns:
^ An under speed error may not necessarily be a fault with the IAC valve. A large friction load on the engine or obstruction in the air intake system could also reduce the engine RPMs.
^ There are four possible sources of friction load that can contribute to under speed error or low idle concerns.
1. Power Steering Load
2. Air Conditioning Load
3. Electrical Load
4. Automatic Transmission Torque Converter Load
EAC Diagnostic Service Tips - Rough Idle
Concerns:
^ Rough idle concerns are often a result of a lean running condition
^ Another possible cause is contamination build up on the MAF sensor
EAC Diagnostic Service Tips - Engine Hard Start/Engine Crank-No Start
^ While performing diagnostics, the technician should ensure that the fuel system is working correctly for all engines with hard start/crank no-start complaints.
^ When diagnosing a mechanical return less fuel system, the following correction to the PC/ED pinpoint HC (4) diagnostic procedure should be used when performing the KEOE fuel pressure test:
^ Perform the KOEO fuel pressure test as specific in the PC/ED manual.
^ The fuel pressure should drop off no more than 10 psi from maximum pressure (no lower than 55 psi for a 65 psi max system or no lower than 45 psi for a 55 psi max system) within 5 minutes of the start of the test.
^ The fuel pressure should drop off to no less than 30 psi within 30 minutes of the start of the test.
^ For greatest accuracy, the service technician should read the fuel pressure as soon as possible after pump shut off, no more than 5 minutes after the start of the test.
NOTE
RETURNABLE AND ELECTRONIC RETURN LESS SYSTEMS SHOULD ALSO BE DIAGNOSED USING THE PROCEDURES LISTED FOR THEM IN PINPOINT TEST HC.
IAC Diagnostic Service Tips - High Idle RPM at Start Up:
^ Most engines will have a temporary high idle at engine start up to allow for catalyst light off. If DTC 1506 is not present, this indicates that there is no fault present with the IAC.
^ A vehicle with very low odometer miles, may exhibit a higher than normal temporary startup fast idle (1600-2500 RPM that decreases slowly). No repairs should be attempted because this is a normal temporary PCM calibration strategy to prevent spark plug fouling during plant/transportation operation. The calibration will permanently revert to its normal strategy after the PCM has seen its first 4 miles of continuous drive cycle. A brand new vehicle may accumulate some mileage without turning this strategy off if the drive cycle has been below 4 miles at a time.
IAC Diagnostic Service Tips - EAC Valve Noise Issues
For IAC valve noise concerns check for obstructed or potentially damaged IAC valve from backfire.
NOTE
ON SOME NEWER MODEL YEAR VEHICLES THE REACTION SPEED OF THE EAC VALVE IS FAST ENOUGH THAT IT MIGHT MAKE A "POPPING" SOUND AS IT REACTS TO A LARGE IDLE LOAD. THIS IS A NORMAL CHARACTERISTIC AND NO ATTEMPTS SHOULD BE MADE IN AN EFFORT TO MODIFY THE PERFORMANCE OF THE IAC VALVE. IF POSSIBLE, COMPARE AGAINST A LIKE VEHICLE.
NOTE
REMEMBER THAT MOST WEATHER SERVICES REPORT A LOCAL BAROMETRIC PRESSURE THAT HAS BEEN CORRECTED TO SEA LEVEL. THE BARO PID, ON THE OTHER HAND, REPORTS THE ACTUAL BAROMETRIC PRESSURE FOR THE ALTITUDE THE VEHICLE IS BEING OPERATED IN. LOCAL WEATHER CONDITIONS (HIGH AND LOW PRESSURE AREAS) WILL CHANGE THE LOCAL BAROMETRIC PRESSURE BY SEVERAL INCHES OF MERCURY (+/- 3 Hz, +/-1 in.Hg.).
NOTE
BARO IS UPDATED ONLY WHEN THE VEHICLE IS AT HIGH THROTTLE OPENINGS. THEREFORE, A VEHICLE, WHICH IS DRIVEN DOWN FROM A HIGHER ALTITUDE MAY NOT HAVE HAD AN OPPORTUNITY TO UPDATE THE BARO VALUE IN KAM. IF YOU ARE NOT CONFIDENT THAT BARO HAS BEEN UPDATED, PERFORM THREE OR FOUR HEAVY, SUSTAINED ACCELERATIONS AT GREATER THAN HALF-THROTTLE TO ALLOW BARO TO UPDATE.