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Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda 6. However, it is still accessible from the selected car via links, so may be relevant.
NO. 8 ENGINE RUNS ROUGH/ROLLING IDLE [AJ] DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1
  • Verify the following:
    • External fuel shut off or accessory (kill switch, alarm etc.)
    • Fuel quality: 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
  • Are all items okay?
 Yes Go to the next step.
No Service as necessary.
2
  • Connect WDS or equivalent to DLC-2.
  • Turn ignition switch to ON position (Engine OFF).
  • Retrieve any DTCs.
  • Are there any DTCs displayed?
 Yes DTC is displayed: 
  • Go to appropriate DTC test.
No No DTC is displayed: 
  • Go to the next step.
3
  • Is engine overheating?
 Yes Go to symptom troubleshooting "NO. 17 COOLING SYSTEM CONCERNS-OVERHEATING ".
No Go to the next step.
4
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 run it at idle.
  • Turn A/C switch on.
  • Measure low side and high side pressures.
  • Are reading pressures within specifications?

    (See REFRIGERANT PRESSURE CHECK .)

 Yes Go to the next step.
No If A/C is always on, go to symptom troubleshooting "NO. 24 A/C ALWAYS ON/A/C COMPRESSOR RUNS CONTINUOUSLY ".
For other symptoms, inspect the following:
  • Refrigerant charging amount
  • Condenser fan operation
5
NOTE:
  • The following test is for engine running rough with P/S on. If other symptoms exist, go to the next step.
  • Start engine and run it at idle
  • Measure voltage at PSP switch terminal A.
  • Is voltage okay?
 Yes Go to the next step.
No Inspect PSP switch operation and wiring harness between PSP switch terminal A and PCM terminal 14.
6
  • Visually inspect CKP sensor and teeth of crankshaft pulley.
  • Are CKP sensor and teeth of crankshaft pulley okay?
 Yes Go to the next step.
No Replace malfunctioning part.
7
  • Inspect ignition coil related harnesses condition (intermittent open or short circuit) for all cylinders.
  • Are all harnesses condition okay?
 Yes Go to the next step.
No Repair suspected wiring harness.
8
  • Inspect spark plug conditions.
  • Is 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 for clogged fuel injector.
No Install spark plugs on original cylinders.
Go to the next step.
9 Yes Go to the next step.
No Repair or replace malfunctioning part according to electronic throttle control system operation inspection results.
10
  • Install fuel pressure gauge between pulsation damper and fuel distributor.
  • Start engine and run it at idle.
  • Measure fuel line pressure at idle.

    (See FUEL LINE PRESSURE INSPECTION .)

  • Is fuel line pressure correct at idle?
 Yes Go to the next step.
No Zero or low: 

High: 
11
  • 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 to OFF position?
 Yes Go to the next step.
No Inspect fuel injector.
(See FUEL INJECTOR INSPECTION [AJ] .)
12
  • Connect WDS or equivalent to DLC-2.
  • Start the engine and run it at idle.
  • Access LONGFT1 and LONGFT2 PID.
  • Measure LONGFT1 and LONGFT2 PID at idle.
  • Is PID value within -15% - +15%
 Yes Go to the next step.
No LONGFT1 and LONGFT2 PID is out of specification.
Less than specification (too rich): 
  • Inspect EVAP control system.
    • If system is okay, go to Step 14.

Greater than specification (too lean): 
  • Inspect for air leakage at intake-air system components.
    • If system okay, go to the next step.
13
  • Disconnect vacuum hose between purge solenoid valve and intake manifold from purge solenoid valve side.
  • Plug opening end of vacuum hose.
  • Start engine.
  • Does engine condition improve?
 Yes Inspect if purge solenoid valve sticks open mechanically.
Inspect EVAP control system.
No Go to the next step.
14
  • Remove and shake PCV valve.
  • Does PCV valve rattle?
 Yes Go to the next step.
No Replace PCV valve.
(See EGR VALVE REMOVAL/INSTALLATION [AJ] .)
15
  • Inspect for restriction in the exhaust system.
  • Is there any restriction?
 Yes Inspect exhaust system.
No Go to the next step.
16
  • Visually inspect CMP sensor and tooth of camshaft pulley.
  • Are CMP sensor and tooth of camshaft pulley okay?
 Yes Go to the next step.
No Replace malfunctioning part.
17
  • Inspect engine condition while tapping EGR valve housing.
  • Does engine condition improve?
 Yes Replace EGR valve.
No Go to the next step.
18 Yes Go to the next step.
No Repair or replace malfunctioning part according to variable valve timing control system inspection results.
19 Yes Inspect valve timing.
No Inspect for causes.
20
  • Verify test results.
    • If okay, return to diagnostic index to service any additional symptoms.
    • 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, reprogram PCM if later calibration is available. Retest.
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