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2008 - MX-5 - Engine

NO.9 FAST IDLE/RUNS ON [LF]



9

FAST IDLE/RUNS ON

DESCRIPTION

  • The engine speed continues at fast idle after warm-up.

  • The engine runs after the ignition switch is turned off.

POSSIBLE CAUSE

  • ECT sensor malfunction

  • Air leakage from intake-air system

  • Throttle body malfunction

  • Accelerator pedal position sensor misadjustment

  • Cruise control system operation improperly

  • Improper load signal input

  • Improper operation of electronic throttle control system


Diagnostic procedure

STEP

INSPECTION

RESULTS

ACTION

1

Connect the M-MDS to the DLC-2.

Access ECT PID.

Start and warm up engine to normal operating temperature.

Is ECT PID between 82—112°C {180—234°F}?

Yes

Go to the next step.

No

ECT PID is higher than 112°C {234°F}:

Go to symptom troubleshooting "No.17 Cooling system concerns - Overheating".

ECT PID is less than 82°C {180°F}:

Go to symptom troubleshooting "No.18 Cooling system concerns - Runs cold".

2

Connect the M-MDS to the DLC-2.

Turn the ignition switch to the ON position (Engine off).

Retrieve any DTCs.

Are there any DTCs displayed?

Yes

DTC is displayed:

Go to the appropriate DTC inspection.

(See DTC TABLE [LF].)

No

No DTC is displayed:

Go to the next step.

3

Access and monitor AC_REQ, CPP (MT), CPP/PNP (MT), and TR (AT) PIDs.

Are PIDs values normal?

(See PCM INSPECTION [LF].)

Yes

Go to the next step.

No

If the AC_REQ PID is not normal:

  • Inspect A/C switch, refrigerant pressure switch, and fan switch, and related wiring harness for vibration or intermittent open/short circuit.

If the CPP PID is not normal:

  • Inspect clutch position switch and related wiring harness for vibration or intermittent open/short circuit.

If the CPP/PNP PID is not normal:

  • Inspect neutral position switch and related wiring harness for vibration or intermittent open/short circuit.

If the TR PID is not normal:

  • Inspect TR switch and related wiring harness for vibration or intermittent open/short circuit.

4

Connect the M-MDS to the DLC-2.

Start the engine and idle it.

Retrieve any DTCs for EHPAS.

Is there any EHPAS DTC displayed?

Yes

DTC is displayed:

Go to appropriate DTC inspection.

No

No DTC is displayed:

Go to the next step.

5

Is there air leakage felt or heard at intake-air system components while racing engine to higher speed?

Yes

Repair or replace parts if necessary.

No

Inspect the following:

  • Electronic throttle control system operation

  • Accelerator pedal position sensor

6

  • Verify test results.

    • If normal, return to diagnostic index to service any additional symptoms.

      (See SYMPTOM DIAGNOSTIC INDEX [LF].)

    • If malfunction remains, inspect related Service Bulletins and/or On-line Repair Information and perform repair or diagnosis.

      • If vehicle is repaired, troubleshooting completed.

      • If vehicle is not repaired or additional diagnostic information is not available, replace the PCM.

        (See PCM REMOVAL/INSTALLATION [LF].)




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