Diagnostic Aids

WARNING: This page is about a different car, the 1995 Ford Ranger. 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.
Wiring harness circuits (SIG RTN, PWR GND and VPWR).
Powertrain Control Module (PCM).

Fig 1: Air Intake Circuit & Components Schematic (Ranger)

1) Confirm Drive Symptom

Test drive vehicle. Check for any of the following symptoms:

Accelerator pedal sticking or binding.
Hard start/long cranking.
Hesitation or stalls at idle.
Rough idle.
Lack of power.

If symptom is present, go to next step. If symptom is not present, fault cannot be duplicated or identified at this time and testing is complete.

2) Check Accelerator Linkage

If linkage sticks, binds or grabs, go to next step. If linkage operation is okay, go to step 7).

3) Turn ignition off. Disconnect accelerator linkage from throttle body. Inspect cable for freedom of travel from accelerator pedal to throttle body linkage cable connector. If cable moves freely, go to next step. If cable does not move freely, repair or replace as necessary.

4) Check Throttle Return Screw

Leave ignition off and accelerator linkage disconnected from throttle body. Remove clean air tube from throttle body. Inspect clean air tube for dirt or contamination, and repair as necessary. Check throttle return screw. If throttle return screw is in contact with throttle linkage lever arm when throttle is fully closed, go to step 6). If throttle screw is not as specified, place a .002" (.05 mm) feeler gauge between throttle return screw and lever arm. Turn screw until it contacts feeler gauge. Remove feeler gauge. Turn throttle adjust screw 1/2 turn clockwise and go to next step.

5) Check TP Sensor Range

Turn ignition off. Connect scan tester to DLC. Using scan tester, access TP PID. While observing TP PID, slowly move throttle from closed to open position. TP PID reading changes should be smooth while rotating throttle. At closed position, TP PID reading should be 0.66-1.20 volts (13-24%). If TP output is as specified, remove scan tester and go to next step. If TP output is not as specified, replace throttle body assembly.

6) Check Throttle Body

Leave ignition off. Disconnect cable from throttle body. Remove clean air tube. 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 throttle moves freely, fault cannot be duplicated or identified at this time and testing is complete. If throttle does not rotate freely, go to next step.

7) Check Air Filter

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

8) Check Engine Operation

Ensure that the following engine systems are in good operating condition before continuing:

Engine cooling system.
Exhaust system.
Fuel pressure.
PCV system.

If systems are operating correctly, go to next step. If systems are not operating correctly, go to CIRCUIT TEST as indicated:

Exhaust system; CIRCUIT TEST HF.
Fuel pressure; CIRCUIT TEST HC.
PCV system; CIRCUIT TEST HG.
Engine cooling system; repair as necessary.

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 or replace as necessary. If no faults are found, go to next step.

10) Check Idle Speed

Turn all accessories off. Start engine and warm to normal operating temperature. Connect scan tester to DLC. Using scan tester, access IAC PID, idle air percent duty cycle. IAC PID reading should be as follows:

Ranger with 4R55E transmission; 20-44 percent with engine idling at 800-850 RPM.
Ranger with M5 transmission; 20-45 percent with engine idling at 725-775 RPM.

If IAC PID values are correct, go to next step. If IAC PID values are not correct, go to step 12).

11) Check Idle Control Pressure

Leave accessories off. With engine operating at idle, goose throttle and return to idle position. If engine stalls or engine speed fluctuates excessively before returning to idle, go to next step. If engine does not stall or fluctuate, air intake system is okay and testing is complete.

12) Check IAC Solenoid Function

Leave accessories off. With engine operating at idle, disconnect IAC solenoid wiring harness connector. If engine speed does not change, replace IAC solenoid and clear Keep Alive Memory. If engine speed changes, proceed as follows:

For vehicles with fast idle symptom, go to next step.
For vehicles without fast idle symptom, check throttle body for malfunction. Repair as necessary and clear Keep Alive Memory (KAM).

13) Check IAC Circuit For Short To Ground

Leave accessories off and IAC solenoid disconnected. Turn ignition off. Disconnect PCM 104-pin connector. Inspect pins for damage and repair if necessary. Install EEC-V Breakout Box (014-000950), leaving PCM disconnected. Measure resistance between test pin No. 83 (IAC) and test pins No. 51 and 103 (PWR GND) at the breakout box. If resistance is 10,000 ohms or more, replace PCM and repeat QUICK TEST. If resistance is less than 10,000 ohms, repair short circuit and repeat QUICK TEST.