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Home >> Mazda >> 2002 >> Tribute LX, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 393 (Symptom Troubleshooting (Engine Control System) AJ) >> No.8 Engine Runs Rough/Rolling Idle >> Diagnostic procedure

Diagnostic procedure

WARNING: This page is about a different car, the 2005 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
ENGINE RUNS ROUGH/ROLLING IDLE - DIAGNOSTIC PROCEDURE

STEP INSPECTION ACTION
1
  • Verify 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, IAC valve
    • Ignition wiring
    • Electrical connections
    • Fuses
    • Smooth operation of throttle valve
  • Are all items okay?
 Yes Go to next step.
No Service as necessary.
Repeat Step 1.
2
  • Connect WDS or equivalent to DLC-2.
  • Turn ignition key to ON (Engine OFF).
  • Retrieve any DTCs.
  • Is "PASSED" displayed?
 Yes No DTC is displayed: 
  • Go to next step.
No DTC is displayed: 
  • Go to appropriate DTC test.
3
  • Is engine overheating?
 Yes Go to symptom troubleshooting in NO.17 COOLING SYSTEM CONCERNS-OVERHEATING .
No Go to next step.
4
NOTE:
  • Following test is for engine running rough idle with A/C on concerns. If other symptoms exist, go to 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 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 following:
  • Refrigerant charging amount
  • Condenser fan operation
5
NOTE:
  • Following test is for engine running rough with P/S on. If other symptoms exist, go to next step.
  • Start engine and run it at idle.
  • Access PSP SW PID.
  • Inspect if PSP SW PID is ON while turning steering wheel right to left.
  • Is PSP SW PID okay?
 Yes Inspect power steering pressure switch operation and wiring harness between power steering pressure switch connector and PCM connector terminal 55.
No Go to next step.
6
  • Visually inspect CKP sensor and teeth of crankshaft pulley.
  • Are CKP sensor and teeth of crankshaft pulley okay?
 Yes Go to next step.
No Replace malfunctioning part
7
  • Inspect ignition coil related harnesses condition (intermittent open or short circuit) for all cylinders.
  • Are all harness condition okay?
 Yes Go to 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 next step.
9
  • Start engine and disconnect IAC valve connector.
  • Does RPM drop or engine stall?
 Yes Go to next step.
No Inspect IAC valve, and wiring harness.
10
  • Install fuel pressure gauge between pulsation damper and fuel distributor.
  • Start engine and run it at idle.
  • Measure fuel line pressure at idle.
  • Is fuel line pressure correct at idle?
Fuel line pressure 420-460 kPa {4.3-4.6 kgf/cm2, 61-66 psi} 		 Yes Go to next step.
No Zero or low: 
  • Inspect fuel pump circuit.
  • Inspect for open fuel pump relief valve
  • Inspect for fuel leakage inside pressure regulator.
  • Inspect for clogged main fuel line.

High: 
  • Inspect pressure regulator for high pressure cause.
  • Inspect for clogged fuel return line.
11
  • Visually inspect for fuel leakage at fuel injector, O-ring, and fuel line.
  • Service as necessary.
  • Does fuel line pressure hold after ignition key is turned to OFF?
 Yes Go to next step.
No Inspect pressure regulator diaphragm condition.
  • If condition is okay, inspect fuel injector.
  • If condition is not okay, replace pressure regulator
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 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.

More than specification (too lean): 
  • Inspect for air leakage at intake-air system components.
  • If system okay, go to 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 next step.
14
  • Remove and shake PCV valve.
  • Does PCV valve rattle?
 Yes Go to next step.
No Replace PCV valve.
15
  • Inspect for restriction in the exhaust system.
  • Is there any restriction?
 Yes Inspect exhaust system.
No Go to next step.
16
  • Visually inspect CMP sensor and tooth of camshaft.
  • Are CMP sensor and tooth of camshaft okay?
 Yes Go to 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 next step.
18 Yes Inspect valve timing.
No Inspect for causes.
19
  • 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, replace or reprogram PCM.
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