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Mazda CX-9 Grand Touring. Manual - part 334

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE [MZI-3.7]

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE (MZI-3.7) DETECTION CONDITIONS AND
POSSIBLE CAUSES

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



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)

2008 Mazda CX-9 Grand Touring

2008 ENGINE Symptom Troubleshooting (MZI-3.7) - Mazda CX-9

Microsoft

Sunday, November 15, 2009 10:10:05 AM

Page 42

DIAGNOSTIC PROCEDURE

NO.8 ENGINE RUNS ROUGH/ROLLING IDLE (MZI-3.7) DIAGNOSTIC PROCEDURE

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 [MZI-3.7] .)

(See AFTER SERVICE PRECAUTION [MZI-3.7] .)

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.

STEP

INSPECTION

RESULTS

ACTION

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.)

Go to the next step.

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

Yes

Go to the next step.

2008 Mazda CX-9 Grand Touring

2008 ENGINE Symptom Troubleshooting (MZI-3.7) - Mazda CX-9

Microsoft

Sunday, November 15, 2009 10:10:05 AM

Page 43



Ignition wiring



Electrical connections



Fuses



Smooth operation of throttle valve



PCM GND circuit (1D, U, 1BP,
1BK)

Are all items normal?

Service if necessary.

Repeat Step 2.

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 [MZI-3.7] .)

No DTC is displayed:

Go to the next step.

Is the engine overheating?

Yes

Go to symptom troubleshooting "No.17
Cooling system concerns - Overheating".
(See NO.17 COOLING SYSTEM
CONCERNS-OVERHEATING [MZI-
3.7].)

Go to the next step.

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.

Inspect for open or short circuit of MAF

sensor and related wiring harness.

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 .)

NOTE:



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

Yes

Go to the next step.

If the A/C is always on, go to symptom

troubleshooting "No.24 A/C is always on

or A/C compressor runs continuously".

(See NO.24 A/C IS ALWAYS ON OR

A/C COMPRESSOR RUNS

CONTINUOUSLY [MZI-3.7].)

For other symptoms, inspect the

following:



Refrigerant charging amount



Condenser fan operation

Connect the M-MDS to the DLC-2.Start

NOTE:



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

Yes

Go to the next step.

Inspect power steering pressure switch

operation and wiring harness between P/S

pressure switch and PCM terminal 21.

2008 Mazda CX-9 Grand Touring

2008 ENGINE Symptom Troubleshooting (MZI-3.7) - Mazda CX-9

Microsoft

Sunday, November 15, 2009 10:10:05 AM

Page 44

the engine and idle it.Access PSP PID.Is
PSP PID within specification?

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.

Replace the malfunctioning part.

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.

Repair the wiring harnesses.

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.

Install the spark plugs on original

cylinders.

Go to the next step.

Perform the electronic throttle control
system operation inspection.
(See ENGINE CONTROL SYSTEM
OPERATION INSPECTION [MZI-
3.7].)
Does the electronic throttle control system
function properly?

Yes

Go to the next step.

Repair or replace the malfunctioning part

according to electronic throttle control

system operation inspection results.

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 [MZI-3.7] .)

Yes

Go to the next step.

Low:

Inspect the fuel line for clogging.

If there is no malfunction, replace fuel

pump unit.

(See FUEL PUMP UNIT

REMOVAL/INSTALLATION [MZI-

3.7] .)
High:

Replace the fuel pump unit.

(See FUEL PUMP UNIT

REMOVAL/INSTALLATION [MZI-

3.7] .)

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 [MZI-3.7] .)

Yes

Go to the next step.

Inspect fuel injector.

If fuel injector is normal, replace fuel

pump unit.

(See FUEL PUMP UNIT

REMOVAL/INSTALLATION [MZI-

3.7] .)

Yes

Go to the next step.

2008 Mazda CX-9 Grand Touring

2008 ENGINE Symptom Troubleshooting (MZI-3.7) - Mazda CX-9

Microsoft

Sunday, November 15, 2009 10:10:05 AM

Page 45

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