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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 DIAGNOSTIC PROCEDURE

STEP INSPECTION RESULTS ACTION
1 Verify the following:
  • External fuel shut off or accessory (such as kill switch, alarm.)
  • Fuel quality (e.g. 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 normal?		 Yes Go to the next step.
No Service if necessary.
Repeat Step 1.
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 idle it.Turn 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 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
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 idle it. 		Yes Go to the next step.
No Inspect power steering pressure switch operation and wiring harness between P/S pressure switch connector and PCM terminal 55(1), 1Z(2).
6 Visually inspect CKP sensor and teeth of crankshaft pulley.
Are CKP sensor and teeth of crankshaft pulley normal?		 Yes Go to the next step.(1)
Go to Step 8.(2)
No Replace malfunctioning parts.
7 Inspect ignition coil related harnesses condition (intermittent open or short circuit) for all cylinders.
Are all harnesses condition normal?		 Yes Go to Step 9.
No Repair suspected wiring harness.
8 Inspect for cracks on high-tension leads.
Are there any cracks on high-tension leads?		 Yes Repair suspected high-tension leads.
No Go to the next step.
9 Inspect spark plug condition.
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.
10 Perform electronic throttle control system operation inspection.
(See ELECTRONIC THROTTLE CONTROL SYSTEM INSPECTION .)
Does electronic throttle control system work properly		 Yes Go to the next step.
No Repair or replace malfunctioning part according to electronic throttle control system operation inspection results.
11 Install fuel pressure gauge between fuel pipe and fuel distributor.
Start engine and idle it.
Measure fuel line pressure during idle.
Is fuel line pressure correct during idle?
(See FUEL LINE PRESSURE INSPECTION .)		 Yes Go to the next step.
No Zero or low: 
Inspect for clogged fuel line.
If okay, replace fuel pump unit.
High: 
Replace fuel pump unit.
12 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 )		 Yes Go to the next step.
No Inspect fuel injector.
If fuel injector is okay, replace fuel pump unit.
13 Connect WDS or equivalent to DLC-2.
Start the engine and idle it.
Access LONG FT1 PID.
Measure LONG FT1 PID during idle.
Is PID value between -14% and +14%? 		 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 okay, go to Step 15.

Greater than specification (too lean):
  • Inspect for air leakage at intake-air system components.
    • If system is okay, go to the next step.
14 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 Check if purge solenoid valve sticks open mechanically.
Inspect EVAP control system.
No Go to the next step.
15 Remove and shake PCV valve.
Does PCV valve rattle		 Yes Go to the next step.
No Replace PCV valve.
16 Inspect for restriction in exhaust system.
Is there any restriction?		 Yes Inspect exhaust system.
No Go to the next step.
17 Visually inspect CMP sensor and teeth of camshaft.
Are CMP sensor and teeth of camshaft normal?		 Yes Go to the next step.
No Replace malfunctioning parts.
18 Inspect engine condition while tapping EGR valve housing.
Does engine condition improve		 Yes Replace EGR valve.
No Go to the next step.
19 Inspect variable valve timing control system operation.
(See VARIABLE VALVE TIMING CONTROL SYSTEM OPERATION INSPECTION .)
Does variable valve timing control system work properly?		 Yes Go to the next step.
No Repair or replace malfunctioning parts.
20 Is engine compression correct Yes Inspect valve timing.
No Inspect for causes.
21 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.
(1) California emission regulation applicable ATX model
(2) Except for California emission regulation applicable ATX model
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