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2008 - MX-5 - Engine

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE [LF]



8

ENGINE RUNS ROUGH/ROLLING IDLE

DESCRIPTION

  • Engine speed fluctuates between specified idle speed and lower speed and engine shakes excessively.

  • Idle speed is too slow and engine shakes excessively.

POSSIBLE CAUSE

  • Air leakage from intake-air system parts

  • A/C system operation is improper

  • Erratic signal to ignition coil

  • Spark plug malfunction

  • Purge solenoid valve malfunction

  • Improper operation of electronic throttle control system

  • Idle learning of electronic throttle control system is not completed

  • EGR valve malfunction

  • Erratic or no signal from CMP sensor

  • Low engine compression

  • Improper valve timing

  • Improper variable valve timing control system operation

  • Erratic signal from CKP sensor

  • Improper air / fuel mixture ratio control operation (abnormal signal form MAF sensor or HO2S)

  • Open or short circuit in PCM GND circuit

  • Poor fuel quality

  • PCV valve malfunction

  • Air cleaner restriction

  • Restriction in exhaust system

  • Disconnected electrical connectors

  • Inadequate fuel pressure

  • Fuel pump body mechanical malfunction

  • Improper load signal input

  • Fuel line restriction or clogging

  • Improper fuel injection control operation

  • Fuel leakage from fuel injector

  • Fuel injector clogging

  • Engine overheating

  • Vacuum leakage

  • Pressure regulator malfunction (built-in fuel pump unit)

WARNING:

The following troubleshooting flow chart contains fuel system diagnosis and repair procedures. Read following warnings before servicing the fuel system:
  • Fuel vapor is hazardous. It can easily ignite, causing serious injury and damage. Always keep sparks and flames away from fuel.

  • Fuel line spills and leakage are dangerous. Fuel can ignite and cause serious injuries or death and damage. Fuel can also irritate skin and eyes. To prevent this, always complete “BEFORE SERVICE PRECAUTION” and “AFTER SERVICE PRECAUTION” described in this manual.

    (See BEFORE SERVICE PRECAUTION [LF].)

    (See AFTER SERVICE PRECAUTION [LF].)

CAUTION:

  • Disconnecting/connecting quick release connector without cleaning it may cause damage to fuel pipe and quick release connector. Always clean quick release connector joint area before disconnecting/connecting, and make sure that it is free of foreign material.


Diagnostic procedure

STEP

INSPECTION

RESULTS

ACTION

1

Warm up the engine.

Idle the engine for 5 min.

Is the symptom disappeared?

Yes

Troubleshooting completed. (Cause of this symptom is that the idle learning of electronic throttle control system is not completed.)

No

Go to the next step.

2

Verify the following:

  • External fuel shut off or accessory (such as kill switch, alarm)

  • Fuel quality (such as proper octane, contamination, winter/summer blend)

  • No air leakage from intake-air system

  • Proper sealing of intake manifold and components attached to intake manifold: EGR valve

  • Ignition wiring

  • Electrical connections

  • Fuses

  • Smooth operation of throttle valve

  • PCM GND circuit (1AZ, 1BB, 1BD, 1BH)

Are all items normal?

Yes

Go to the next step.

No

Service if necessary.

Repeat Step 2.

3

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.

4

Is the engine overheating?

Yes

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

No

Go to the next step.

5

Connect the M-MDS to the DLC-2.

Access MAF PID.

Drive vehicle with monitoring PID. Is MAF PID within specification?

Yes

Go to the next step.

No

Inspect for open or short circuit of MAF sensor and related wiring harness.

6

NOTE:

  • The following test is for engine running at rough idle with A/C on. If other symptoms exist, go to the next step.

Connect pressure gauge to A/C low and high pressure side lines.

Start engine and idle it.

Turn the A/C switch on.

Measure low side and high side pressures.

Are pressures within specifications?

(See REFRIGERANT PRESSURE CHECK.)

Yes

Go to the next step.

No

If the A/C is always on, go to symptom troubleshooting "No.24 A/C is always on or A/C compressor runs continuously".

For other symptoms, inspect the following:

  • Refrigerant charging amount

  • Condenser fan operation

7

NOTE:

  • The following test is for engine running rough with P/S on. If other symptoms exist, go to the next step.

Connect the M-MDS to the DLC-2.

Start the engine and idle it.

Retrieve any DTCs for EPS.

Is there any EPS DTC displayed?

Yes

Go to appropriate the DTC inspection.

(See DTC TABLE [LF].)

No

Go to the next step.

8

Visually inspect the CKP sensor and teeth of crankshaft pulley.

Are the CKP sensor and teeth of crankshaft pulley normal?

Yes

Go to the next step.

No

Replace the malfunctioning part.

9

Inspect the ignition coil related wiring harness condition (intermittent open or short circuit) for all cylinders. Are wiring harness conditions normal?

Yes

Go to the next step.

No

Repair the wiring harnesses.

10

Inspect the spark plug condition.

Is the spark plug wet, covered with carbon or grayish white?

Yes

Spark plug is wet or covered with carbon:

Inspect for fuel leakage from injector.

Spark plug is grayish white:

Inspect the fuel injector for clogging.

No

Install the spark plugs on original cylinders.

Go to the next step.

11

Perform the electronic throttle control system operation inspection.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does the electronic throttle control system function properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part according to electronic throttle control system operation inspection results.

12

Install fuel pressure gauge between fuel pipe and fuel distributor.

Start the engine and run it at idle.

Measure fuel line pressure during idle.

Is fuel line pressure correct during idle?

(See FUEL LINE PRESSURE INSPECTION [LF].)

Yes

Go to the next step.

No

Low:

Inspect the fuel line for clogging.

If there is no malfunction, replace fuel pump unit.

(See FUEL PUMP UNIT REMOVAL/INSTALLATION [LF].)

High:

Replace the fuel pump unit.

(See FUEL PUMP UNIT REMOVAL/INSTALLATION [LF].)

13

Visually inspect for fuel leakage at fuel injector, O-ring, and fuel line.

Service if necessary.

Does fuel line pressure hold after ignition switch is turned off?

(See FUEL LINE PRESSURE INSPECTION [LF])

Yes

Go to the next step.

No

Inspect fuel injector.

If fuel injector is normal, replace fuel pump unit.

14

Connect the M-MDS to the DLC-2.

Start the engine and idle it.

Access LONG FT1 PID.

Measure LONG FT1 PID at idle.

Is PID value normal? (See PCM INSPECTION [LF].)

Yes

Go to the next step.

No

LONG FT1 PID is out of specification.

Less than specification (too rich):

  • Inspect EVAP control system.

    • If system is normal, go to Step 16.

Greater than specification (too lean):

  • Inspect for air leakage at intake-air system components.

    • If system is normal, go to the next step.

15

Disconnect the vacuum hose between the purge solenoid valve and the intake manifold from purge solenoid valve side.

Plug opening end of vacuum hose.

Start the engine.

Does the engine condition improve?

Yes

Check if purge solenoid valve is stuck open mechanically.

Inspect EVAP control system.

No

Go to the next step.

16

Remove and shake the PCV valve.

Does the PCV valve rattle?

Yes

Go to the next step.

No

Replace the PCV valve.

17

Visually inspect the exhaust system part.

Is there any deformed exhaust system part?

Yes

Replace the suspected part.

No

Go to the next step.

18

Visually inspect the CMP sensor and teeth of camshaft.

Are the CMP sensor and teeth of camshaft normal?

Yes

Go to the next step.

No

Replace the malfunctioning part.

19

Inspect the engine condition while tapping EGR valve housing.

Does the engine condition improve?

Yes

Replace the EGR valve.

No

Go to the next step.

20

Inspect variable valve timing control system operation.

(See ENGINE CONTROL SYSTEM OPERATION INSPECTION [LF].)

Does variable valve timing control system function properly?

Yes

Go to the next step.

No

Repair or replace the malfunctioning part.

21

Is engine compression correct?

Yes

Inspect the valve timing.

(See VARIABLE VALVE TIMING ACTUATOR INSPECTION [LF].)

No

Inspect for causes.

22

  • 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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