Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 86

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–339

ROUGH, UNSTABLE, OR INCORRECT IDLE, STALLING SYMPTOM

DEFINITIONS: Engine runs unevenly at idle. If severe,
the engine or vehicle may shake. Engine idle speed may
vary in RPM. Either condition may be severe enough to
stall the engine.

                                                                                    X

                                                     

time

rpm

Rough Idle

Stall

Step

Action

Value(s)

Yes

No

1

Was the “On-Board Diagnostic (OBD) System Check”
performed?

—

Go to Step 2

Go to On Board 

Diagnostic 

(OBD) System 

Check

2

1. Perform a bulletin search. 

2. If a bulletin that addresses the symptom is found,

correct the condition as instructed in the bulletin. 

Was a bulletin found that addresses the symptom?

—

Verify repair

Go to Step 3

3

Was a visually/physical check performed?

—

Go to Step 4

Go to Visual / 

physical Check

4

Is the customer using the incorrect fuel type? 

Diesel fuel 

only

Replace with 

diesel fuel

Go to Step 5

5

1. Check for incorrect idle speed. Ensure that the

following conditions are present. 

• Engine fully warm. 

• Accessories are “OFF”. 

2. Using a Tech 2, monitor “Desired Engine Idle

Speed” and “Engine Speed”. 

Is the “Engine Speed” within the specified values?

Desired 

Engine Idle 

Speed ± 25 

rpm

Go to Step 7

Go to Step 6

6

Visually/physically inspect for the following conditions. 

• Restrict air intake system. Check for a restricted air

filter element, or foreign objects blocking the air
intake system 

• Check for objects blocking or excessive deposits in

the throttle bore and on the throttle plate 

• Check for a condition that causes a large vacuum

leak, such as an incorrectly installed or faulty
crankcase ventilation hose. 

• Restrict air intake system at the turbocharger.

Check for objects blocking the turbocharger
compressor wheel or turbine shaft sticking. 

If a problem is found, repair as necessary. 
Was a problem found?

—

Verify repair

Go to Step 7

7

Check the ECM & PSG grounds to verify that they are
clean and tight. Refer to the ECM wiring diagrams. 
Was a problem found?

—

Verify repair

Go to Step 8

6E–340

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

8

1. Using the Tech 2, ignition “On” and engine “Off”. 

2. Monitor the “Neutral Switch” in the data display. 

Does the Tech 2 indicate correct “Neutral Switch”
status depending on any shift positions? 
If a problem is found, repair as necessary. 
Was the problem found?

—

Verify repair

Go to Step 9

9

1.  Using the Tech 2, ignition “On” and engine “Run”. 

2. Monitor the “A/C Information Switch” in the data

display. 

Does the Tech 2 indicate correct “A/C Information
Switch” status depending on A/C switch position? 
If a problem is found, repair as necessary. 
Was the problem found?

—

Verify repair

Go to Step 10

10

1. Using the Tech 2, display the ECT sensor and IAT

sensor value. 

2. Check the displayed value. 

Does the Tech 2 indicate correct temperature
depending on engine condition? 
If a problem is found, repair as necessary. 
Was the problem found?

—

Verify repair

Go to Step 11

11

1. Using the Tech 2, ignition “On” and engine “Run”. 

2. Monitor the “Mass Air Flow” in the data display. 

Does the Tech 2 indicate correct “Mass Air Flow”
depending on accelerator pedal operation? 

—

Go to Step 16

Go to Step 12

12

Remove the MAF & IAT sensor assembly and check
for the following conditions. 

• Objects blocking at the MAF sensor element. 
If a problem is found, repair as necessary. 
Was the problem found?

—

Verify repair

Go to Step 13

13

Check the MAF sensor harness for the following
conditions. 

• Check for poor connector connection. 

• Check for misrouted harness. 

• Check for any accessory parts which may cause

electric interference. 

If a problem is found, repair as necessary. 
Was a problem found? 

—

Verify repair

Go to Step 14

14

Substitute a known good MAF & IAT sensor assembly
and recheck. 
Was the problem solved?

—

Go to Step 15

Go to Step 36

15

Replace the MAF & IAT sensor assembly. 
Is the action complete?

—

Verify repair

—

16

1. Using the Tech 2, ignition “On” and engine “Off”. 

2. Monitor the “Pedal/Throttle Position” and “Idle

Switch” in the data display. 

Does the Tech 2 indicate correct “Pedal/Throttle
Position” from 0% to 100% and correct “Idle Switch”
status depending on accelerator pedal operation?

—

Go to Step 21

Go to Step 17

Step

Action

Value(s)

Yes

No

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

6E–341

17

1. Using the Tech 2, ignition “On” and engine “Off”. 

2. Monitor the “Pedal/Throttle Position” and “Idle

Switch” in the data display. 

3. Adjust the accelerator cable or TPS within 0% to

100%. 

Was the problem solved?

—

Verify repair

Go to Step 18

18

Check the TPS harness for the following conditions. 

• Check for poor connector connection. 

• Check for misrouted harness. 

• Check for any accessory parts which may cause

electric interference. 

If a problem is found, repair as necessary. 
Was a problem found? 

—

Verify repair

Go to Step 19

19

Substitute a known good TPS and recheck. 
Was the problem solved?

—

Go to Step 20

Go to Step 36

20

Replace the TPS. 
Is the action complete?

—

Verify repair

—

21

Remove the CKP sensor from the flywheel housing
and check for the following conditions. 

• Objects sticking the CKP sensor. 

• Objects sticking the CKP sensor pulser. 
If a problem is found, repair as necessary. 
Was the problem found? 

—

Verify repair

Go to Step 22

22

Check the CKP sensor harness for the following
conditions. 

• Check for poor connector connection. 

• Check for misrouted harness. 

• Check for any accessory parts which may cause

electric interference. 

If a problem is found, repair as necessary. 
Was a problem found? 

—

Verify repair

Go to Step 23

23

Substitute a known good CKP sensor and recheck.                                                                                              
Was the problem solved?

—

Go to Step 24

Go to Step 25

24

Replace the CKP sensor. 
Is the action complete?

—

Verify repair

—

Step

Action

Value(s)

Yes

No

6E–342

4JA1-TC/4JH1-TC ENGINE DRIVEABILITY AND EMISSIONS

25

1. Using the Tech 2 and ignition “On” and engine

“Run”. 

2. Monitor the following parameters in the data

display. 

• “Desired Injection Quantity” & “Injection Quantity” 

• “Desired Injection Start” &  “Actual Injection Start” 
Are the large gap or unstable parameter displayed
between “Desired” and “Actual”?

—

Go to Step 29

Go to Step 26

26

Using the vacuum pump and check the EGR valve (if
equipped) operation for the following condition through
the small window. 

• Restrict shaft movement. Check for objects sticking

the shaft, broken diaphragm or excessive carbon
deposit. 

If a problem is found, repair as necessary. 
Was a problem found? 

—

Verify repair

Go to Step 27

Step

Action

Value(s)

Yes

No

         When idling or part-throttle

                                               

                                               

High

Desired

Low

Time

    Actual

Vacuum Pump

Small Window