Diagnostic Aids

WARNING: This page does not describe the selected car, but rather 26 other vehicles, including the 1999 Mercury Tracer, 1999 Mercury Sable, 1999 Mercury Mystique, 1999 Mercury Mountaineer, and 1999 Mercury Grand Marquis. However, it is still accessible from the selected car via links, so may be relevant.

Perform this test when instructed during QUICK TEST or if directed by other test procedures. This test is used to diagnose the following:

Accelerator linkage.
Air cleaner assembly.
Air inlet tube.
Clean air tube and resonator.
Throttle body assembly.
IMRC actuator assembly.
Intake Manifold Runner Control (IMRC) assembly.
Wiring harness circuits (IMRC, IMRC MONITOR, SIG RTN, PWR GND and VPWR).
Powertrain Control Module (PCM).

1) Check For Incorrect Idle Speed

Ensure engine is at normal operating temperature. Start engine and allow to idle. Check idle speed. If idle speed is correct, go to next step. If idle speed is high, check if throttle arm fully returns and contacts return stop. Repair as necessary and go to step 6). If idle speed is low, go to step 7).

2) Check Accelerator Linkage

If linkage sticks, binds or grabs, go to next step. If linkage operation is okay, go to step 4).

3) Inspect Accelerator/Speed Control Cables

Turn ignition off. Disconnect accelerator and speed control cables from throttle body. Inspect cables for freedom of travel from accelerator pedal/speed control device to throttle body linkage cable connector. If cables move freely, go to next step. If cables do not move freely, repair as necessary.

4) Check Functionality Of Throttle Position (TP) Sensor

Turn ignition on. Using scan tool, select TP V PID from PID/DATA monitor menu. While observing PID reading, slowly open throttle to full wide open position. If PID voltage reading indicates a smooth reading during throttle movement, go to next step. If PID voltage reading does not indicate a smooth reading, replace TP sensor.

5) Check Air Filter

Check air filter. Clean or replace filter as necessary. If air filter is okay, go to next step.

6) Check Positive Crankcase Ventilation (PCV) System

A high idle may indicate incorrect PCV valve size or a vacuum leak. Check PCV valve connections for leaks or cracks. Remove PCV valve and check for plugged or incorrect valve. Repair as necessary. If PCV valve is okay reinstall PCV valve and go to step 9) (high idle concerns) or go to next step (all others).

7) Check IAC Solenoid Function

Ensure all accessories are off. With engine operating at idle, disconnect IAC solenoid connector. If engine speed decreases or engine stalls, go to next step. If engine speed does not change, go to step 9) (high idle concern) or replace IAC solenoid (low idle concern).

8) Check For Plugged Throttle Body Plate Hole

Remove resonator from throttle body assembly. Inspect throttle plate hole for restriction. Repair as necessary. If throttle plate does not have a hole, or hole is not plugged, go to TROUBLE SHOOTING - NO CODES - EEC-V article and diagnose by symptom.

9) Check For Vacuum Leaks

Start engine and allow to idle. Inspect inlet air system from MAF sensor to intake manifold for cracks, loose connections or faulty gaskets. Inspect intake manifold, EGR diaphragm and vacuum hoses for leaks. Repair as necessary. If no faults are found, go to next step.

10) Check Throttle Body

Turn ignition off. Remove throttle body. With throttle fully closed, ensure light cannot be seen between throttle bore and plate. Snap throttle from wide open to closed position several times. Slowly cycle throttle from closed to wide open position. Check for freedom of travel especially during initial throttle opening. If faults are present, replace throttle body. If throttle body is okay, fault cannot be duplicated or identified at this time. Reinstall throttle body and check for additional symptoms and repair as necessary. See TROUBLE SHOOTING - NO CODES - EEC-V article.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 10) to step 15). No test procedures have been omitted.

15) DTC P1516, P1517, P1518, P1519, P1520, P1537 & P1538

DTCs P1516 and P1517 indicate control input error. DTCs P1518 indicates IMRC stuck open. DTC P1519 indicates IMRC stuck closed. DTC P1520 indicates control circuit failure. DTC P1537 indicates bank 1 stuck open. DTC P1538 indicates bank 2 stuck open. Possible causes are:
- Faulty vacuum hoses.
- Faulty vacuum solenoid.
- Faulty vacuum actuator.
- Cables improperly routed, binding or seized.
- Damaged or disconnected IMRC housing return springs.
- Lever return stop obstructed or bent.
- Lever wide open stop obstructed or bent.
- IMRC actuator cable or gears seized.
On models with electric IMRC system, visually inspect IMRC cables for correct routing. Ensure cable core wire has slack at IMRC housing and stop screw contacts lever. On Escort and Tracer, ensure actuator lever is visible. On models with vacuum operated IMRC system, ensure sensor linkage is attached and secure. With engine running, lever must contact closed plate stop screw. On all models, operate IMRC plates while checking for binding and sticking. If any faults are found, repair as necessary. If no faults are found, go to next step.

16) IMRC Test

On Escort and Tracer, remove IMRC actuator assembly. On all other models, disconnect IMRC linkage or cable(s) from intake runner(s). On all models, rotate IMRC lever(s) while checking for binding or sticking. Feel for return spring tension. Levers should fully open and close without obstruction. If any faults are found, repair as necessary. If no faults are found, replace IMRC actuator.

17) Perform IMRC Function Test

Turn ignition on. If IMRC plates open immediately when ignition is turned on, go to step 23). If IMRC plates do not open immediately, using scan too, access OUTPUT TEST MODE. Turn all outputs on. When IMRC is commanded on, lever(s) should rotate to full open position. One or both levers should contact wide open stop (one lever being slightly off is acceptable). On Escort and Tracer, IRMC actuator lever should rotate to full open position at about 90 degrees. On all models, IMRC levers should cycle fully from closed to open position. If IMRC levers do not operate as specified, go to next step. If IMRC levers operate as specified, go to step 25).

18) Check IMRC Voltage

Turn ignition off. Disconnect IMRC actuator connector. Turn ignition on. Measure voltage between VPWR terminal at IMRC actuator wiring harness connector and negative battery terminal. See Fig 1-Fig 4 . If voltage is more than 10.5 volts, go to step 20) (Escort and Tracer) or go to next step (all other models). If voltage is 10.5 volts or less, repair open in VPWR circuit.
NOTE: IMRC actuator harness connector may also be referred to as IMRC harness connector.

Fig 1: Identifying IMRC Actuator Wiring Harness Connector Terminals (Escort & Tracer)
Courtesy of FORD MOTOR CO.

Fig 2: Identifying IMRC Wiring Harness Connector Terminals (Econoline 4.2L, Pickup 4.2L & Windstar 3.8L)
Courtesy of FORD MOTOR CO.

Fig 3: Identifying IMRC Wiring Harness Connector Terminals (Contour 2.5L, Cougar 2.5L, Mystique 2.5L, Sable 3.0L 4-Valve, Taurus 3.0L 4-Valve & Taurus SHO)
Courtesy of FORD MOTOR CO.

Fig 4: Identifying Intake Manifold Tuning (IMT) Valve Vacuum Solenoid Wiring Harness Connector Terminals (Econoline 5.4L, Expedition 4.6L & 5.4L, Navigator 5.4L, Pickup 4.6L & 5.4L)
Courtesy of FORD MOTOR CO.

19) Check For Open Circuit

Measure voltage between VPWR terminal and SIG RTN terminal at IMRC actuator wiring harness connector. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, repair open in SIG RTN circuit.

20) Verify Driver Circuit

Turn ignition off. Connect a test light between VPWR terminal and IMRC SIGNAL terminal at IMRC actuator wiring harness connector. Test light should be off. Using scan tool, access OUTPUT TEST MODE. Turn all outputs on. If test light is now on, go to step 32). If test light is still off, go to next step.

21) Check For Open IMRC Driver Circuit

Disconnect PCM 104-pin connector. Measure resistance between PCM connector pin No. 42 and IMRC SIGNAL terminal at IMRC actuator wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in IMRC SIGNAL circuit.

22) Check For Short To Power

Turn ignition on. Measure voltage between IMRC SIGNAL terminal at actuator wiring harness connector and ground. If voltage is less than 10.5 volts, replace PCM. If voltage is 10.5 volts or more, repair short to power.

23) Check IMRC Circuit Driver For Short Circuit

Ensure PCM is connected. Measure resistance between IMRC SIGNAL terminal and SIG RTN and PWR GND terminals at IMRC actuator wiring harness connector. Also measure resistance between IMRCM terminal and SIG RTN and PWR GND terminals at IMRC actuator wiring harness connector. If all resistance readings are more than 10,000 ohms, replace IMRC actuator. If any resistance reading is 10,000 ohms or less, go to next step.

24) Identify Fault

Disconnect PCM connector. Measure resistance between IMRC SIGNAL terminal and SIG RTN and PWR GND terminals at IMRC actuator wiring harness connector. Also measure resistance between IMRCM terminal and SIG RTN and PWR GND terminals at IMRC actuator wiring harness connector. If all resistance readings are more than 10,000 ohms, replace PCM. If any resistance reading is 10,000 ohms or less, repair short in appropriate circuit.

25) Check IMRC Monitor PID

Using scan tool, select IMRCM PID from PID/DATA monitor menu. On models with 3.8L or 4.2L, PID value should be about 2.5 volts. On all other models, PID value should be about 4.5 volts. On all models, if PID voltage is as specified, go to next step. If PID voltage is not as specified, go to step 30).

26) Identify Short Circuit

Using scan tool, access OUTPUT TEST MODE. Access IMRCM PID. Turn all outputs on. If PID value is less than one volt, go to next step. If PID value is one volt or less, go to step 32).

27) Check For Short To Power In IMRC Monitor Circuit

Disconnect IMRC actuator connector. Turn ignition on. Measure voltage between IMRCM terminal at IMRC actuator wiring harness connector and negative battery terminal. If voltage is more than 10.5 volts, go to next step. If voltage is 10.5 volts or less, go to step 29).

28) Check For Short With PCM Disconnected

Turn ignition off. Disconnect PCM connector. Turn ignition on. Measure voltage between IMRCM terminal at IMRC actuator wiring harness connector and negative battery terminal. If voltage is more than 10.5 volts, repair short in IMRCM circuit. If voltage is 10.5 volts or less, replace PCM.

29) Check For IMRC Actuator Short

Turn ignition off. Measure resistance between VPWR terminal and IMRCM terminal at IMRC actuator wiring harness connector. If resistance is more than 10,000 ohms, no fault is indicated at this time. Go to TEST Z and check for intermittents. If resistance is 10,000 ohms or less, replace IMRC actuator.

30) Check For Short To Ground

Ensure ignition is on. Using scan tool, select IMRCM PID from PID/DATA monitor menu. Note PID voltage reading. Disconnect IMRC actuator connector. If PID voltage changed from less than one volt to about 4.5 volts, replace IMRC actuator. If voltage does not change from less than one volt to about 4.5 volts, go to next step.

31) Check For Short To Ground With PCM Disconnected

Turn ignition off. Measure resistance between IMRCM terminal at IMRC actuator wiring harness connector and ground. If resistance is more than 10,000 ohms, replace PCM. If resistance is 10,000 ohms or less, repair short in IMRCM circuit.

32) Check IMRC Monitor Circuit Response

Turn ignition off. Disconnect IMRC actuator connector. Turn ignition on. Using scan tool, select IMRCM PID from PID/DATA monitor menu. Note PID voltage reading. Connect a jumper wire between IMRCM terminal at IMRC actuator wiring harness connector and ground. If PID voltage changed from about 4.5 volts to less than one volt, go to next step. If PID voltage did not change from about 4.5 volts to less than one volt, go to step 36).

33) Check Circuit Continuity

Turn ignition off. Measure resistance between negative battery terminal and SIG RTN or CHASSIS GROUND terminal at IMRC actuator wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, go to step 35).

34) Wiggle Test

Ensure ignition is off. Measure resistance of IMRCM circuit between PCM connector pin No. 8 and IMRC actuator wiring harness connector. A fault will be indicated by change in resistance reading. Wiggle wiring harness between IMRC actuator connector and PCM connector. If fault is indicated, isolate fault and repair as necessary. If no faults are indicated, replace IMRC actuator.

35) Check Circuit Continuity With PCM Disconnected

Disconnect PCM connector. Measure resistance of SIG RTN or CHASSIS GROUND terminal at IMRC actuator wiring harness connector and PCM connector. If resistance is less than 5 ohms, replace PCM. If resistance is 5 ohms or more, repair open in SIG RTN or CHASSIS GROUND circuit.

36) Check IMRC Monitor Circuit Continuity

Disconnect PCM connector. Measure resistance between PCM connector pin No. 8 and IMRCM terminal at IMRC actuator wiring harness connector and PCM connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in IMRCM circuit.

37) Check For Intermittent Fault

Ensure ignition is off. Measure resistance of IMRCM circuit between PCM connector pin No. 8 and IMRC actuator wiring harness connector. A fault will be indicated by change in resistance reading. Wiggle wiring harness between IMRC actuator connector and PCM connector. If fault is indicated, isolate fault and repair as necessary. If no faults are indicated, replace PCM.

38) IMRC Repair Verification Drive Cycle

Clear PCM memory. Using scan tool, select IMRC, IMRCM and RPM PIDs. Test drive vehicle. Complete 3 accelerations from a complete stop to a speed requiring engine speed of more than 3500 RPM. Watch for PID values to change. Stop vehicle. Repeat QUICK TEST and retrieve all DTCs. If any DTCs are present, go to appropriate system test. If no DTCs are present, testing is complete.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 38) to step 65). No test procedures have been omitted.

65) DTC P1549: Check IMT Valve & Vacuum Actuator Connection

This fault indicates IMTV circuit fault. Possible causes are:
- VPWR circuit open.
- Open or shorted signal circuit.
- Faulty IMT valve.
- Faulty Powertrain Control Module (PCM).
Turn ignition off. Check IMT valve system. Ensure wiring harness connector is installed properly. Repair as necessary. If no faults are found, go to next step.

66) Check PCM Driver Command

Start engine. Using scan tool, select IMTV PID from PID/DATA monitor menu. Observe PID value and increase engine speed to about 3500 RPM. PID value should indicate 100 percent then drop to 50 percent when engine RPM is more than 3500. If PID value is as specified, PCM driver command is okay. Go to next step. If PID value is not as specified, replace PCM.

67) Check For Open IMT Valve Actuator Or Vacuum Solenoid VPWR Circuit

Turn ignition off. Disconnect IMT valve actuator connector. See Fig 4. Turn ignition on. Measure voltage between chassis ground and VPWR terminal at IMT valve actuator wiring harness connector. If voltage is more than 10.5 volts, go to step 69). If voltage is 10.5 volts or less, repair open in VPWR circuit.
NOTE: A break in step numbering sequence occurs at this point. Procedure skips from step 67) to step 69). No test procedures have been omitted.

69) Check For Open Circuit

Turn ignition off. Disconnect PCM 104-pin connector. Inspect for damaged pins and repair if necessary. Measure resistance between PCM connector pin No. 46 and IMT VALVE SIGNAL terminal at IMT valve actuator wiring harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in IMT VALVE SIGNAL circuit.

70) Check IMT Valve Actuator Signal Circuit For Short To PWR GND

Measure resistance between PCM connector pin No. 46 and pin No. 77 or 103. If resistance is more than 10,000 ohms, go to next step. If resistance is 10,000 ohms or less, repair IMT VALVE SIGNAL circuit short to PWR GND circuit.

71) Check IMT VALVE SIGNAL Circuit For Short To VPWR

Turn ignition on. Measure voltage between PCM connector pin No. 46 and pin No. 77 or 103. If voltage is one volt or more, repair IMT VALVE SIGNAL circuit short to VPWR. If voltage is less than one volt, go to next step.

72) Check PCM Driver

Turn ignition off. Reconnect PCM connector. Connect a DVOM between ground and VPWR terminal at IMT valve actuator wiring harness connector. Turn ignition on. Voltage should be less than one volt. Using scan tool, access OUTPUT TEST MODE. Turn all outputs on. DVOM voltage reading should change to more than 10.5 volts. If voltage is not as specified, replace PCM. If voltage is as specified, go to next step.

73) Check IMT Valve Shutter

Remove IMT valve. Check IMT valve shutter for damage. Rotate shutter and check for binding. Replace IMT valve as necessary. If IMT valve is okay, leave IMT valve disassembled and go to next step.

74) Check IMT Valve Actuator

Reconnect IMT valve actuator connector. Turn ignition on. Using scan tool, access OUTPUT TEST MODE. Observe IMT valve shutter and turn all outputs on. If shutter rotates, no fault is indicated at this time. Go to TEST Z . If shutter does not rotate, replace IMT valve actuator. Verify symptom is no longer present.