Lexus NX: Rough Idling

DESCRIPTION

Problem Symptom	Suspected Area	Trouble Area
Engine speed fluctuation due to abnormal combustion Idle speed too low or high Strong engine vibration due to above symptoms	Ignition malfunction Deviation in air fuel ratio (Excessive or insufficient intake air volume or fuel supply) Insufficient compression Changes in load from another system	Ignition system	Spark plug Ignition coil assembly
		Fuel system	Fuel injector assembly Fuel pump Fuel pump control circuit Fuel line Purge VSV system Fuel quality (existence of foreign matter, degradation)
		Intake and exhaust systems	EGR system Mass air flow meter sub-assembly Intake system (Air leaks or deposit accumulation) Throttle body with motor assembly Air fuel ratio sensor Heated oxygen sensor Camshaft timing oil control assembly Variable Valve Timing system (VVT system)
		Other control systems	ECM Wire harness or connector Knock control sensor Engine coolant temperature sensor
		Engine	Thermostat Engine assembly Engine mount

SYMPTOM AND CAUSE OF SYSTEM MALFUNCTION

HINT:

The following are descriptions of the characteristics of each system malfunction. After understanding the link between the causes and symptoms, perform the inspection of each component. Even if the problem symptom does not recur, signs of the malfunction may be found in the Data List.

(a) Ignition system

Spark plug

Main cause of malfunction	Performance degradation (wear, existence of foreign matter, etc.)
Symptom	Engine speed fluctuation due to abnormal combustion
Data List	Cylinder Misfire Count
HINT: If the spark plug of the malfunctioning cylinder is abnormally wet with fuel, a leaking fuel injector assembly is suspected.

Ignition coil assembly

Main cause of malfunction	Internal malfunction
Problem symptom	Engine speed fluctuation due to abnormal combustion
Data List	Cylinder Misfire Count

(b) Fuel system

Fuel injector assembly

Main cause of malfunction	Blockage
Problem symptom	Engine speed fluctuation due to abnormal combustion Idle speed too low or high
Data List	Short FT Long FT Fuel System Status Target Air-Fuel Ratio AF Lambda A/F Learn Value Idle A/F Learn Value Low A/F Learn Value Mid1 A/F Learn Value Mid2 A/F Learn Value High Total FT
HINT: If the engine malfunction disappears when the fuel injection volume is increased or decreased using the Control the Injection Volume, the respective cylinder may be malfunctioning.

Fuel system

HINT: If the air fuel ratio becomes lean only when the engine is running under a high load and at a high engine speed, clogging of the fuel pump or fuel filter is suspected.

Fuel quality

Main cause of malfunction	Fuel degradation due to age or water contamination Low fuel quality Addition of fuel additive
Problem symptom	Engine speed fluctuation due to abnormal combustion Idle speed too low or high Engine is difficult to start

(c) Intake and exhaust systems

EGR system

Main cause of malfunction	EGR valve movement problems or stuck
Problem symptom	Engine speed fluctuation due to abnormal combustion Idle speed too low or high Startability malfunction, lack of power or engine stalls
Data List	EGR Step Position Target EGR Position Normally, Actual EGR Position = Target EGR Position +/-5%(fully open: 0%, fully closed: 100%) When the power switch is turned on (IG), the EGR valve fully closes.

Mass air flow meter sub-assembly

Main cause of malfunction	Performance degradation (existence of foreign matter, etc.)
Problem symptom	Lack of power
Data List	MAF
HINT: If the value of the Data List item "MAF" is abnormal, a malfunction of the mass air flow meter sub-assembly is suspected.

Throttle system

Main cause of malfunction	Inappropriate trim volume adjustment due to accumulation of deposits
Problem symptom	Engine speed fluctuation due to abnormal combustion Idle speed too low or high
Data List	ISC Learning Value ISC Flow ISC Feedback Value Electric Load Feedback Val Air Conditioner FB Val

Air fuel ratio sensor, Heated oxygen sensor

Main cause of malfunction	Deviation in sensor characteristics
Problem symptom	Abnormal combustion due to deviation of actual air fuel ratio from calculated ratio
Data List	AFS Voltage O2S Fuel System Status

(d) Engine

Engine assembly

Main cause of malfunction	Compression loss Accumulation of deposits (Combustion chamber, intake valve or intake manifold)
Problem symptom	Engine speed fluctuation due to abnormal combustion Idle speed too low or high Hesitation during acceleration or stalling
HINT: If deposits have accumulated in the combustion chamber or on an intake valve, the engine may stall when deposits are caught on an intake valve. When performing the Active Test "Check the Cylinder Compression", if the speed of one cylinder is higher than the others, the cylinder may have a compression loss. If deposits accumulate on the intake valves, the supply of fuel may be delayed due to adherence of the fuel to the deposits, causing a rough idle.

Data List Items Related to Rough Idling

HINT:

Depending on the vehicle model, the applicable Data List items may vary. Data List items other than the ones used in the diagnostic procedure are for reference only.

PROCEDURE

1.	INTERVIEW THE CUSTOMER

(a) Interview the customer for details about the conditions when the rough idle occurred.

HINT:

Depending on the conditions when the rough idle occurred, a malfunction in one of the following areas is suspected.

Problem Symptom	Suspected Area
Improper running of the engine in particular by idling after it is started cold, and improper running is felt less after the engine speed is increased.	Possibly caused by excessive EGR due to defective closing of the EGR valve
Hesitation or lack of power occurs during acceleration, regardless of whether engine is cold or warm	For low mileage vehicles (ODO reading of less than approximately 20000 km or yearly mileage of less than 2000 km): Fuel quality (degradation, water contamination, etc.) For high mileage vehicles (ODO reading of more than approximately 150000 km): Excessively lean air fuel ratio during acceleration due to deposits in intake system or combustion chamber caught temporarily on intake or exhaust valve or adherence of fuel to the deposits Abnormal mass air flow meter sub-assembly output due to existence of foreign matter Decrease in fuel injector assembly injection volume due to low quality fuel
Engine stalls or is difficult to start immediately after engine stalled, regardless of whether engine is cold or warm	Deposits in intake system or combustion chamber caught temporarily on intake or exhaust valve

NEXT

2.	CHECK DTC OUTPUT

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Perform a road test.

(e) Enter the following menus: Powertrain / Engine and ECT / Trouble Codes.

(f) Read the DTCs.

Powertrain > Engine and ECT > Trouble Codes

Result	Proceed to
DTCs are not output	A
DTC is output (DTCs other than P1604 or P1605 are output)	B

B

GO TO DTC CHART

A

3.	SYMPTOM CONFIRMATION

(a) Check if the problem symptoms reported in the customer problem analysis recur.

HINT:

If the problem symptoms do not recur, attempt to reproduce the conditions when the malfunction occurred based on the result of the customer problem analysis.

Result	Proceed to
The problem symptom recurs	A
The problem symptom does not recur (occurred in the past)	B

B

CHECK FOR INTERMITTENT PROBLEMS

A

4.	READ VALUE USING TECHSTREAM (ISC LEARNING VALUE)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / ISC Learning Value.

Powertrain > Engine and ECT > Data List

Tester Display
ISC Learning Value

(e) Read the value displayed on the Techstream.

Result	Proceed to
Less than 7.0 L/s	A
Other than above	B

B

GO TO STEP 17

A

5.	READ VALUE USING TECHSTREAM (SHORT FT AND LONG FT)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Enter the following menus: Powertrain / Engine and ECT / Data List / All Data / Short FT and Long FT.

(e) Read the value displayed on the Techstream.

Data List	Result	Proceed to
Short FT + Long FT	-15% or higher, or less than 15%	A
	Other than above	B

B

GO TO STEP 15

A

6.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE CYLINDER FUEL CUT)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine.

HINT:

Reproduce the vehicle conditions when the malfunction occurred (such as after the engine is warmed up or after a cold start).

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Cylinder Fuel Cut / All Data / Engine Speed.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the Cylinder Fuel Cut

Data List Display
Engine Speed

(g) According to the display on the Techstream, perform the Active Test and check for a malfunctioning cylinder.

Result	Proceed to
One cylinder is malfunctioning	A
Multiple or all cylinders are malfunctioning, or the malfunctioning cylinder cannot be determined.	B

B

GO TO STEP 13

A

7.	PERFORM ACTIVE TEST USING TECHSTREAM (CHECK THE CYLINDER COMPRESSION)

HINT:

If the vehicle does not support the Active Test "Check the Cylinder Compression", measure the compression pressure. If the compression pressure is normal, go to step 8.

(a) Warm up the engine.

(b) Turn the power switch off.

(c) Connect the Techstream to the DLC3.

(d) Turn the power switch on (IG).

(e) Turn the Techstream on.

(f) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(g) Enter the following menus: Powertrain / Engine and ECT / Active Test / Check the Cylinder Compression.

Powertrain > Engine and ECT > Active Test

Tester Display
Check the Cylinder Compression

HINT:

To display the entire Data List, press the pull down menu button next to Primary. Then select Compression.

(h) While the engine is not running, press the RIGHT or LEFT button to change Check the Cylinder Compression to ON.

HINT:

After performing the above procedure, Check the Cylinder Compression will start. Fuel injection for all cylinders is prohibited and each cylinder engine speed measurement enters standby mode.

(i) Crank the engine for about 10 seconds.

(j) Monitor the engine speed (Engine Speed of Cyl and Av Engine Speed of All Cyl) displayed on the Techstream.

HINT:

At first, the Techstream displays extremely high cylinder engine speed values. After approximately 10 seconds of engine cranking, each cylinder engine speed measurement will change to the actual engine speed.

(k) Stop cranking the engine, and then change "Check the Cylinder Compression" to OFF after the engine stops.

(l) Read the value.

Result	Proceed to
There is no variation in "Engine Speed of Cyl" (All cylinders display approximately the same value for "Engine Speed of Cyl")	A
There is variation in "Engine Speed of Cyl" (Only one cylinder displays a value for "Engine Speed of Cyl" that differs considerably)	B

B

GO TO STEP 12

A

8.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature 75°C (167°F) or higher with all the accessories switched off.

(f) Idle the engine.

(g) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor.

Powertrain > Engine and ECT > Active Test

Tester Display
Control the Injection Volume for A/F Sensor

(h) According to the display on the Techstream, perform the Active Test and check the vehicle conditions when increasing and decreasing the fuel injection volume.

HINT:

Change the fuel injection volume between the minimum and maximum range of correction (e.g. -12.5% to 12.5%).

Result	Proceed to
Malfunction is still present even if the fuel injection volume is changed	A
Malfunction disappears when the fuel injection volume is changed	B

B

GO TO STEP 11

A

9.	CHECK IGNITION SYSTEM

(a) Check the ignition system.

Result	Proceed to
The malfunctioning cylinder does not return to normal	A
The malfunctioning cylinder returned to normal	B

B

GO TO STEP 22

A

10.	INSPECT OTHER RELATED COMPONENTS

(a) Check the ignition coil assembly power source circuit, wire harness and connectors.

NEXT

GO TO STEP 22

11.	REPLACE FUEL INJECTOR ASSEMBLY

(a) Replace the fuel injector assembly of the malfunctioning cylinder.

Click here

NEXT

GO TO STEP 24

12.	CHECK CYLINDER COMPRESSION PRESSURE

(a) Measure the cylinder compression pressure. If the compression pressure of a cylinder is low, inspect the engine assembly and repair or replace parts as necessary. .

Click here

HINT:

Perform "Inspection After Repair" after repairing or replacing the engine mechanical system.

NEXT

GO TO STEP 24

13.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE EGR STEP POSITION)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

HINT:

The A/C switch and all accessory switches should be off.

(f) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the EGR Step Position / Primary / MAP and Throttle Idle Position.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the EGR Step Position

Data List Display
MAP
Throttle Idle Position

(g) Confirm that the Throttle Idle Position is ON and check the MAP values in the Data List while performing the Active Test.

Result	Proceed to
MAP increases by less than 10 kPa (75 mmHg) when the EGR valve is fully closed (0 step)	A
MAP increases by 10 kPa (75 mmHg) or more when the EGR valve is fully closed (0 step)	B

B

GO TO STEP 15

A

14.	REPLACE EGR VALVE ASSEMBLY

(a) Replace the EGR valve assembly.

Click here

NEXT

GO TO STEP 24

15.	READ VALUE USING TECHSTREAM (MAF)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature 75°C (167°F) or higher with all the accessories switched off.

(f) Enter the following menus: Powertrain / Engine and ECT / Data List / MAF.

Powertrain > Engine and ECT > Data List

Tester Display
MAF

(g) According to the display on the Techstream, read the Data List when the power switch is turned on (IG) and while maintaining an engine speed of 2500 rpm.

Result	Proceed to
Power switch on (IG) (engine stopped): 0.58 gm/sec or higher	A
Engine speed 2500 rpm (without load): Less than 5.0 gm/sec
Other than above	B

B

GO TO STEP 19

A

16.	CHECK INTAKE SYSTEM

(a) Check for air leaks or blockage in the intake system components. If a connection problem or foreign matter is found, repair the connection or remove the foreign matter.

NEXT

GO TO STEP 24

17.	REMOVE FOREIGN OBJECT (CLEAN THROTTLE BODY WITH MOTOR ASSEMBLY)

(a) Clean off any deposits from the inside of the throttle body with motor assembly.

(b) Push open the throttle valve and wipe off any carbon from the valve and bore using a piece of cloth soaked in non-residue solvent.

*1	Throttle Body with Motor Assembly	*2	Bore
*3	Valve	-	-
*a	Reference	*b	Throttle Body with Motor Assembly Cross-section Diagram
*c	When valve fully opened	*d	Do not directly apply cleaner
*e	Deposits	-	-

HINT:

The illustrations are for reference only. Actual parts may differ.

NEXT

18.	PERFORM CONFIRMATION DRIVING PATTERN

(a) Perform "Inspection After Repair" after cleaning the throttle body with motor assembly.

Click here

(b) Connect the Techstream to the DLC3.

(c) Turn the power switch on (IG).

(d) Turn the Techstream on.

(e) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(f) Start the engine and warm it up until the engine coolant temperature reaches 75°C (167°F) or higher.

(g) Allow the engine to idle for 3 minutes or more and confirm that the engine speed is within the specified range.

HINT:

If the engine is operated without performing learning value reset and idle learning after cleaning the deposits from the throttle body with motor assembly, the idle speed may increase.

NEXT

GO TO STEP 24

19.	PERFORM ACTIVE TEST USING TECHSTREAM (CONTROL THE INJECTION VOLUME FOR A/F SENSOR)

(a) Connect the Techstream to the DLC3.

(b) Turn the power switch on (IG).

(c) Turn the Techstream on.

(d) Put the engine in inspection mode (maintenance mode).

Click here

Powertrain > Hybrid Control > Utility

Tester Display
Inspection Mode

(e) Start the engine and warm it up until the engine coolant temperature 75°C (167°F) or higher with all the accessories switched off.

(f) Warm up the air fuel ratio sensor at an engine speed of 2500 rpm for 90 seconds.

(g) Idle the engine.

(h) Enter the following menus: Powertrain / Engine and ECT / Active Test / Control the Injection Volume for A/F Sensor / All Data / AFS Voltage B1S1 and O2S B1S2.

Powertrain > Engine and ECT > Active Test

Active Test Display
Control the Injection Volume for A/F Sensor

Data List Display
AFS Voltage B1S1
O2S B1S2

(i) According to the display on the Techstream, perform the Active Test and check the vehicle conditions when increasing and decreasing the fuel injection volume.

HINT:

The Control the Injection Volume for A/F Sensor operation lowers the fuel injection volume by 12.5% or increases the injection volume by 12.5%.

Techstream Display (Sensor)	Injection Volume	Voltage
AFS Voltage B1S1 (Air fuel ratio)	12.5%	Below 3.1 V
	-12.5%	Higher than 3.4 V
O2S B1S2 (Heated oxygen)	12.5%	Higher than 0.55 V
	-12.5%	Below 0.4 V

Result	Proceed to
Malfunction disappears when fuel injection volume is increased	A
Malfunction is still present when fuel injection volume is increased, even if output voltage values are normal	B
Output voltage values are abnormal	C

B

GO TO STEP 21

C

GO TO STEP 23

A

20.	REPLACE FUEL INJECTOR ASSEMBLY

(a) Replace the fuel injector assemblies of all cylinders.

Click here

HINT:

Perform "Inspection After Repair" after replacing the fuel injector assembly.

Click here

NEXT

GO TO STEP 24

21.	INSPECT OTHER RELATED COMPONENTS

(a) Inspect other related components.

HINT:

If the malfunctioning part could not be determined by performing the preceding inspections, one of the following malfunctions is suspected.

NEXT

22.	REPAIR OR REPLACE MALFUNCTIONING PARTS

(a) Repair or replace the malfunctioning part.

(b) Perform "Inspection After Repair" after repairing or replacing the malfunctioning part.

NEXT

GO TO STEP 24

23.	REPLACE AIR FUEL RATIO SENSOR AND HEATED OXYGEN SENSOR

(a) Replace the air fuel ratio sensor.

Click here

HINT:

Perform "Inspection After Repair" after replacing the air fuel ratio sensor.

Click here

(b) Replace the heated oxygen sensor.

Click here

HINT:

Perform "Inspection After Repair" after replacing the heated oxygen sensor.

Click here

NEXT

24.	CONDUCT CONFIRMATION TEST

(a) Check that the idle has returned to normal.

NEXT

END

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