1998 Ford Escort engine high idle

Tiny
TONY P34
  • MEMBER
  • 1998 FORD ESCORT
  • 4 CYL
  • FWD
  • MANUAL
  • 150,000 MILES
My engine is at constant high idle about 1300 revs I have replaced iacv and no change.I have checked for vacum leaks useing carb cleaner but no leaks. The voltage at the iacv is 10.85 with engine running it should be 7-9 volts allso when I unplug it the idle drops just below 1000 revs. Please help.
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Friday, April 10th, 2009 AT 6:00 AM

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Tiny
ZACKMAN
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Here is the procedure for testing IAC valve. Don't worry about the break in steps.

CIRCUIT TEST KE - IDLE AIR CONTROL (IAC) VALVE

Turn ignition off. Disconnect IAC valve connector. Turn ignition on. Measure voltage between VPWR terminal at IAC valve wiring harness connector and battery ground terminal. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in VPWR circuit.


http://www.2carpros.com/forum/automotive_pictures/55316_98escortfig52_1.jpg



3) Check IAC Valve Resistance
Turn ignition off. Connect DVOM positive lead to VPWR terminal at IAC valve. Connect DVOM negative lead to IAC terminal at IAC valve. If resistance is 6-13 ohms, go to next step. If resistance is not 6-13 ohms, replace IAC valve assembly.

4) Check IAC Valve Internal Short To Case
Turn ignition off. Measure resistance between each IAC valve terminal and IAC housing. If both resistance readings are more than 10,000 ohms, go to next step. If any resistance reading is 10,000 ohms or less, replace IAC valve assembly.

5) Check Air Inlet System
Turn ignition off. Remove air filter. Inspect air filter, MAF sensor and air inlet system for excessive dirt or contamination. Repair as necessary. If air inlet system is okay, go to next step.

6) Check For Vacuum Leaks
Start engine and allow to idle. Inspect air inlet system any of the following possible faults:
- Cracked or punctured air inlet tube.
- Loose inlet air tube or air cleaner housing.
- Loose or damaged throttle body.
- Contaminated or damaged IAC valve assembly.
- Faulty EGR valve or gasket.
- Faulty PCV valve or hose.
Check entire system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to next step.

7) Check IAC Circuit Continuity
Turn ignition off. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between breakout box test pin No. 83 (IAC) and IAC terminal at IAC valve wiring harness connector. If resistance is 5 ohms or more, repair open in IAC circuit. If resistance is less than 5 ohms, go to next step.

8 ) Check IAC Circuit For Short To Power
Turn ignition on. Measure voltage between test pin No. 83 (IAC) at breakout box and chassis ground. If voltage is one volt or more, repair short to power in IAC circuit. If voltage is less than one volt, go to next step.

9) Check IAC Circuit For Short To Ground
Turn ignition off. Disconnect scan tool from DLC. Measure resistance between test pin No. 83 (IAC) and test pins No. 51 and 103 (PWR GND) at breakout box. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair short to ground in IAC circuit.

10) Check IAC Signal From PCM
Connect PCM to breakout box. Connect IAC valve to wiring harness connector. Connect DVOM between test pins No. 83 (IAC) and No. 51 (PWR GND) at breakout box. Start engine and slowly increase speed to 3000 RPM. If voltage is not 3.0-11.5, replace PCM. If voltage is 3.0-11.5 volts, proceed as follows:
- If Continuous Memory DTC P1504 or P1507 is present, go to step 30).
- If Continuous Memory DTC P1504 or P1507 is not present, check throttle body for damage.
Repair as necessary. If throttle body is okay, replace IAC valve.

20) DTC P1506 This DTC indicates IAC system has reached over speed malfunction. Possible causes are:
IAC circuit short to ground.
IAC assembly stuck open.
Air intake leaks or restrictions.
Damaged throttle body.
Contaminated or damaged IAC valve assembly.
Faulty Powertrain Control Module (PCM).
Start engine and allow to idle. Inspect air inlet system any of the following possible faults:
Cracked or punctured air inlet tube.
Loose inlet air tube or air cleaner housing.
Loose or damaged throttle body.
Contaminated or damaged IAC valve assembly.
Faulty EGR valve or gasket.
Faulty PCV valve or hose.
Check entire system for vacuum leaks. Repair as necessary. If no vacuum leaks are found, go to next step.

21) Check EVAP System Turn ignition off. Disconnect hoses from EVAP canister purge valve. Connect a vacuum pump to carbon canister hose port. See Fig. 53. Using vacuum pump, apply 16 in. Hg to port. If vacuum bleeds off within 20 seconds, replace EVAP canister purge valve. If vacuum holds, go to next step.


http://www.2carpros.com/forum/automotive_pictures/55316_98escortfig53_1.jpg



22) Check IAC Valve Function
Start engine and allow to idle. Ensure transmission is in Park or Neutral and engine is warmed to normal operating temperature. Disconnect IAC valve wiring harness connector. If engine speed drops, go to next step. If engine speed does not drop, check throttle body for damage. If throttle body is okay, replace IAC valve.

23) Check IAC Circuit For Short To Ground
Turn ignition off. Disconnect scan tool from DLC. Disconnect PCM 104-pin connector. Inspect connector for loose, damaged or corroded terminals. Repair as necessary. Install Breakout Box (014-00950), leaving PCM disconnected. Measure resistance between test pin No. 83 (IAC) and test pins No. 51 and 103 (PWR GND) at breakout box. If both resistance readings are more than 10,000 ohms and idle speed is normal, go to step 30). If both resistance readings are more than 10,000 ohms and high idle speed is present, replace PCM. If resistance is 10,000 ohms or less, repair short to ground in IAC circuit.

25) DTC P1505: Check Inlet Air Supply
This DTC indicates IAC system has reached the adaptive learning limit. Possible causes are:
Air intake leaks or restrictions.
Throttle body linkage binding.
Contaminated or damaged IAC valve assembly.
Damaged throttle body.
Inspect air intake system for leaks. Repair as necessary. If air intake system is okay, go to next step.

26) Check Air Inlet System Turn ignition off. Remove air filter. Inspect air filter, MAF sensor and air inlet system for excessive dirt or contamination. Repair as necessary. If air intake system is okay, go to next step.

27) Check Throttle Body & Linkage
Disconnect accelerator cable. Remove air cleaner tube from throttle body. Check cable and throttle body linkage for binding or interference.

30) Check IAC System For Intermittent Open Or Short Circuit Connect scan tool to DLC. Start engine and allow to idle. Ensure all accessories are off and engine is warmed to normal operating temperature. Using scan tool, select IAC and RPM PIDs from PID/DATA monitor menu. IAC duty cycle should be 20-45 percent. Observe IAC and RPM PIDs for indication of fault while performing the following:
- Wiggle and bend wiring harness starting at IAC valve and work toward PCM.
- Lightly tap on IAC valve to simulate road shock.
Fault will be indicated by sudden change in IAC PID or RPM PID value. If any faults are found, isolate fault and repair as necessary. If no faults are found, problem cannot be duplicated at this time.
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Friday, April 10th, 2009 AT 12:31 PM

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