F2–186
TROUBLESHOOTING
NO.8 ENGINE RUNS ROUGH/ROLLING IDLE
A6E408018881210
Diagnostic Procedure
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
• Poor fuel quality
• Air leakage from intake-air system
• Intake-air system restriction
• Incorrect idle speed
• Engine overheating
• Cooling fan No.1 system malfunction
• A/C system improper operation
• EGR system improper operation
• EGR water cooler malfunction
• Fuel leakage
• Inadequate fuel pressure
• Fuel pressure sensor or related circuit malfunction
• Suction control valve malfunction (built-in supply pump)
• Fuel pressure limiter malfunction (built-in common rail)
• Fuel filter clogging
• Fuel line restriction
• Incorrect fuel injection timing
• Erratic signal from CKP sensor
• Erratic signal from CMP sensor
• ECT sensor or related circuit malfunction
• Idle switch misadjustment
• Idle switch or related circuit malfunction
• Accelerator position sensor misadjustment
• Accelerator position sensor or related circuit malfunction
• MAF/IAT sensor malfunction
• Neutral switch or related circuit malfunction
• Supply pump malfunction
• Fuel injector malfunction
• Low engine compression
• Improper valve timing
• Engine compression excessive unbalance for each cylinder
• Unbalanced fuel injection amount for each cylinder
• IDM or related circuit malfunction
Warning
The following troubleshooting flow chart contains the fuel system diagnosis and repair
procedures. Read the following warnings before performing the fuel system services:
• 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 injury or death
and damage. Fuel can also irritate skin and eyes. To prevent this, always complete “BEFORE
REPAIR PROCEDURE” and “AFTER REPAIR PROCEDURE” described in this manual.
STEP INSPECTION RESULTS ACTION
1 Inspect for following:
• Fuel quality (e.g.: including water
contamination, winter/summer blend)
• Fuel line/fuel filter clogging
• Loose bands on intake-air system
• Cracks on intake-air system parts
• Intake-air system restriction
• Vacuum leakage
• Cooling fan No.1 system operation
Are all items okay?
Yes Go to next step.
No Service as necessary
Repeat Step 1.
2 Is engine overheating? Yes Go to symptom troubleshooting “NO.17 COOLING
SYSTEM CONCERNS—OVERHEATING.”
No Go to next step.
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