Mitsubishi Lancer Evolution IX. Manual - part 429

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-191

OPERATION

• The power is supplied to the idle speed control 

servo (terminal No. 2 and No. 5) from the engine 
control relay (terminal No. 4).

• The engine-ECU (terminal No. 14, No. 15, No. 28 

and No. 29) makes power transistor in the unit be 
in "ON" position in order, and that makes currents 
go on the idle speed control servo (terminal No. 
1, No. 3, No. 4 and No. 6).

FUNCTION

• The idle speed control servo opens and closes 

the servo valve in response to a signal from the 
engine-ECU to control the intake air flow rate dur-
ing idling.

TROUBLE JUDGMENT

Check Conditions

• Vehicle speed has reached 1.5 km/h at least 

once.

• Under the closed loop idle speed control.

Judgment Criterion

• Actual idle speed has continued to be higher than 

the target idle speed by 300 r/min. or more for 10 
seconds.

Check Conditions

• Vehicle speed has reached 1.5 km/h at least 

once.

• During idle speed closed loop control.

• The highest temperature at the last drive is 45°C 

or less.

• Engine coolant temperature is approximately 

80

°C or less.

• Battery voltage is 10 V or more.

• The barometric pressure is 76 kPa or higher.

• Intake air temperature is −10°C or more.

Judgment Criterion

• Actual idle speed has continued to be higher than 

the target idle speed by 200 r/min. or more for 10 
seconds.

Check Conditions

• During idle speed closed loop control.

• Engine coolant temperature is approximately 

80

°C or less.

• Battery voltage is 10 V or more.

• Power steering fluid pressure switch is off.

• Volumetric efficiency is 40% or lower.

• The barometric pressure is 76 kPa or higher.

• Intake air temperature is −10°C or more.

Judgment Criterion

• Actual idle speed has continued to be higher than 

the target idle speed by 100 r/min. or more for 10 
seconds.

PROBABLE CAUSES

• Failed idle speed control servo

• Open/short circuit in idle speed control servo cir-

cuit or loose connector contact

• Failed engine-ECU

DIAGNOSIS PROCEDURE

STEP 1. M.U.T.-II/III data list

• Refer to Data List Reference Table 

P.13A-372

.

a. Item No. 45: Idle speed control servo

Q: Is the check result normal?

YES : 

Intermittent malfunction (Refer to GROUP 

00 

− How to Use 

Troubleshooting/Inspection Service Points 

P.00-5

).

NO : 

Go to Step 2 .

STEP 2. Connector check: B-104 idle speed 
control servo connector

Q: Is the check result normal?

YES : 

Go to Step 3 .

NO : 

Repair or replace the connector.

STEP 3. Check idle speed control servo itself.

• Check idle speed control servo itself (Refer to 

P.13A-408

).

Q: Is the check result normal?

YES : 

Go to Step 4 .

NO : 

Replace the idle speed control servo.

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-192

STEP 4. Perform voltage measurement at B-104 
idle speed control servo connector.

• Disconnect connector, and measure at harness 

side.

• Ignition switch: "ON"

• Voltage between terminal No. 2 and earth, also 

between terminal No. 5 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 6 .

NO : 

Go to Step 5 .

STEP 5. Connector check: B-12X engine control 
relay connector

Q: Is the check result normal?

YES : 

Check and repair harness between B-104 

(terminal No. 2 or No. 5) idle speed control 
servo connector and B-12X (terminal No. 4) 
engine control relay connector.

• Check power supply line for 

open/short circuit.

NO : 

Repair or replace the connector.

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

AK305003

2

1

3

4

AB

Connector : B-12X

B-12X

Harness side 
connector

Relay box’s
triangle marks

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-193

STEP 6. Perform voltage measurement at C-121 
engine-ECU connector.

• Disconnect connector, and measure at harness 

side.

• Ignition switch: "ON"

• Voltage between terminal No. 14 and earth, 

between terminal No. 15 and earth, between ter-
minal No. 28 and earth, also voltage between ter-
minal No. 29 and earth.

OK: System voltage

Q: Is the check result normal?

YES : 

Go to Step 7 .

NO : 

Check and repair harness between B-104 

idle speed control servo and C-121 
engine-ECU.

1. Harness between idle speed control 

servo terminal No. 1 and 
engine-ECU connector terminal No. 
14

2. Harness between idle speed control 

servo terminal No. 3 and 
engine-ECU connector terminal No. 
28

3. Harness between idle speed control 

servo terminal No. 4 and 
engine-ECU connector terminal No. 
15

4. Harness between idle speed control 

servo terminal No. 6 and 
engine-ECU connector terminal No. 
29

• Check power supply line for 

open/short circuit.

STEP 7. Connector check: C-121 engine-ECU 
connector

Q: Is the check result normal?

YES : 

Go to Step 8 .

NO : 

Repair or replace the connector.

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

TROUBLESHOOTING

MULTIPORT FUEL INJECTION (MPI)

13A-194

STEP 8. Check harness between B-104 idle 
speed control servo and C-121 engine-ECU 
connector.

1. Harness between idle speed control servo termi-

nal No. 1 and engine-ECU connector terminal 
No. 14

2. Harness between idle speed control servo termi-

nal No. 3 and engine-ECU connector terminal 
No. 28

3. Harness between idle speed control servo termi-

nal No. 4 and engine-ECU connector terminal 
No. 15

4. Harness between idle speed control servo termi-

nal No. 6 and engine-ECU connector terminal 
No. 29

• Check output line for damage.

Q: Is the check result normal?

YES : 

Go to Step 9 .

NO : 

Repair the damaged harness wire.

STEP 9. Check harness between B-104 (terminal 
No. 2 or No. 5) idle speed control servo 
connector and B-12X (terminal No. 4) engine 
control relay connector.

• Check power supply line for damage.

Q: Is the check result normal?

YES : 

Go to Step 10 .

NO : 

Repair the damaged harness wire.

STEP 10. M.U.T.-II/III data list

• Refer to Data List Reference Table 

P.13A-372

.

a. Item No. 45: Idle speed control servo

Q: Is the check result normal?

YES : 

Intermittent malfunction (Refer to GROUP 

00 

− How to Use 

Troubleshooting/Inspection Service Points 

P.00-5

).

NO : 

Replace the engine-ECU.

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

AK501995

2

3

4

5

6

7

8

9

11

12

13

14

15

16

17

18

19

20

30

21

22

23

24

25

26

27

28

29

31

32

33

34

35

1

10

AB

Connector: C-121

C-121 (GR)

C-121 (GR)

Harness side connector

<L. H. drive vehicles>

<R. H. drive vehicles>

AK305029

1

2

3

4

5

6

B-104 (B)

AB

Harness side 
connector

Connector : B-104

AK305003

2

1

3

4

AB

Connector : B-12X

B-12X

Harness side 
connector

Relay box’s
triangle marks