Lexus RX (RX 350L, RX450h) 2016-2024 Repair Manual: Rough Idling

HINT:

• If any other DTCs are output, perform troubleshooting for those DTCs first.
• Make sure to reproduce the conditions present when the malfunction occurred.
• Using the Techstream, read the Data List to confirm the engine operating conditions. This information can be useful when troubleshooting.
• If the problem symptoms do not recur, attempt to reproduce the symptoms and conditions when the malfunction occurred based on the result of the customer problem analysis. Place the priority on confirming the symptoms.

• Compression Leakage Count
• Rough Idle Status
• Plural Cylinders Rough Idle
• Rough Idle Cylinder #1
• Rough Idle Cylinder #2
• Rough Idle Cylinder #3
• Rough Idle Cylinder #4
• Rough Idle Cylinder #5
• Rough Idle Cylinder #6
• Engine Stall Control F/B Flow
• ISC F/B Learn Torque
• ISC Total AUXS Torque
• ISC F/B Torque
• Sum of ISC F/B Torque (Recent)
• ISC AUXS Torque (Alternator)
• ISC AUXS Torque (Air Conditioner)
• Throttle Air Flow F/B Value
• Short FT B1S1, B2S1
• Long FT B1S1, B2S1
• Fuel System Status Bank 1, Bank 2
• Target Air-Fuel Ratio
• A/F (O2) Lambda Sensor B1S1, B2S1
• A/F Learn Value Idle (Port) Bank 1, Bank 2
• A/F Learn Value Low (Port) Bank 1, Bank 2
• A/F Learn Value Mid No.1 (Port) Bank 1, Bank 2
• A/F Learn Value Mid No.2 (Port) Bank 1, Bank 2
• A/F Learn Value High (Port) Bank 1, Bank 2
• A/F Learn Value Idle Bank 1, Bank 2
• A/F Learn Value Low Bank 1, Bank 2
• A/F Learn Value Mid No.1 Bank 1, Bank 2
• A/F Learn Value Mid No.2 Bank 1, Bank 2
• A/F Learn Value High Bank 1, Bank 2
• A/F Learn Value Low (Dual/Port) Bank 1
• A/F Learn Value Low (Dual) Bank 2
• A/F Learn Value Mid (Dual/Port) No.1 Bank 1
• A/F Learn Value Mid (Dual) No.1 Bank 2
• A/F Learn Value Mid (Dual/Port) No.2 Bank 1
• A/F Learn Value Mid (Dual) No.2 Bank 2
• A/F Learn Value High (Dual/Port) Bank 1
• A/F Learn Value High (Dual) Bank 2
• Total FT Bank 1, Bank 2
• Fuel Pressure (High)
• Fuel Pressure (Low) / Fuel Pressure 2
• High Pressure Fuel Pump Duty Ratio (D4)
• Target Fuel Pressure (High)
• Target Fuel Pressure (Low) / Target Fuel Pressure 2
• High Pressure Fuel Pump Discharge Rate
• Mass Air Flow Sensor
• Misfire Count Cylinder #1 to #6
• A/F (O2) Sensor Voltage B1S1, B2S1
• O2 Sensor Voltage B1S2, B2S2

HINT:

• "Total FT Bank 1 (Bank 2)" is used to detect an abnormal air fuel ratio. As the value of "Total FT Bank 1 (Bank 2)" are corrected by the ECM before it is displayed in the Data List, the displayed value may not be equal to the sum of the measured "Short FT B1S1 (B2S1)" and "Long FT B1S1 (B2S1)".
• An abnormally lean or rich tendency can be checked by reading the following Data List items: A/F Learn Value Idle (Port) Bank 1, A/F Learn Value Idle (Port) Bank 2, A/F Learn Value Low (Port) Bank 1, A/F Learn Value Low (Port) Bank 2, A/F Learn Value Mid No.1 (Port) Bank 1, A/F Learn Value Mid No.1 (Port) Bank 2, A/F Learn Value Mid No.2 (Port) Bank 1, A/F Learn Value Mid No.2 (Port) Bank 2, A/F Learn Value High (Port) Bank 1, A/F Learn Value High (Port) Bank 2, A/F Learn Value Idle Bank 1, A/F Learn Value Idle Bank 2, A/F Learn Value Low Bank 1, A/F Learn Value Low Bank 2, A/F Learn Value Mid No.1 Bank 1, A/F Learn Value Mid No.1 Bank 2, A/F Learn Value Mid No.2 Bank 1, A/F Learn Value Mid No.2 Bank 2, A/F Learn Value High Bank 1, A/F Learn Value High Bank 2, A/F Learn Value Low (Dual/Port) Bank 1, A/F Learn Value Low (Dual) Bank 2, A/F Learn Value Mid (Dual/Port) No.1 Bank 1, A/F Learn Value Mid (Dual) No.1 Bank 2, A/F Learn Value Mid (Dual/Port) No.2 Bank 1, A/F Learn Value Mid (Dual) No.2 Bank 2, A/F Learn Value High (Dual/Port) Bank 1 and A/F Learn Value High (Dual) Bank 2. (For vehicles equipped with a V type engine, check that both banks have the same correction tendency.) If the correction of either bank is -15% or less or 15% or higher, the air fuel ratio sensor or heated oxygen sensor of that bank may be malfunctioning.
• The following may cause a lean air fuel ratio (an operating range in which the air fuel ratio learned value correction is 15% or higher):
  1. Decrease in fuel injector assembly injection volume
  2. Decrease in mass air flow meter sub-assembly output (due to existence of foreign matter)
  3. Air leaks in intake system after mass air flow meter sub-assembly
  4. Decrease in fuel pressure (at fuel filter, fuel pump, fuel main valve assembly or fuel suction plate sub-assembly)
• On vehicles which the learning value for each operating range can be checked, if the value of "A/F Learn Value High (Port) Bank 1 (Bank 2)", "A/F Learn Value High Bank 1 (Bank 2)", "A/F Learn Value High (Dual/Port) Bank 1" or "A/F Learn Value High (Dual) Bank 2" only is corrected to the positive side, a malfunction in the fuel system (clogging of the fuel pump or fuel filter) is suspected.
• On vehicles which the learning value for each operating range can be checked, if the value of "A/F Learn Value Idle (Port) Bank 1 (Bank 2)", "A/F Learn Value Low (Port) Bank 1 (Bank 2)", "A/F Learn Value Idle Bank 1 (Bank 2)", "A/F Learn Value Low Bank 1 (Bank 2)", "A/F Learn Value Low (Dual/Port) Bank 1" or "A/F Learn Value Low (Dual) Bank 2" only is corrected to the positive side, an air leak after the mass air flow meter sub-assembly is suspected.
• The following may cause a rich air fuel ratio (an operating range in which the air fuel ratio learned value correction is -15% or less):
  1. Increase in the fuel injector assembly injection volume
  2. Purge VSV system

HINT:

• Perform fuel-cut of port injection and direct injection for each cylinder and check the change in the engine speed.
• If the engine speed of a cylinder does not change while performing the Active Test, it can be determined that the cylinder is malfunctioning.
• If the engine speed of all cylinders change while performing the Active Test, it can be determined that multiple cylinders are malfunctioning.
• A cylinder for which the Data List item "Misfire Count Cylinder #1 to #6" increases may be malfunctioning.
• If "Compression Leakage Count" in the Data List increases, misfiring due to insufficient compression may be occurring.
• When switching the injection method and performing the "D-4S (Fuel Cut)" Active Test, switch from "Port" to "Direct".
• Do not switch from "Direct" to "Port". When performing the inspection more than once, after the Active Test ends, lightly race the engine, and then perform the inspection from "Port" again.
• If the display does not switch from "Port" even after lighting racing the engine, idle the engine for approximately 1 minute, and then lightly race the engine.

HINT:

• At first, the Techstream will display extremely high cylinder engine speed values. After approximately 10 seconds of engine cranking, the engine speed measurement of each cylinder will change to the actual engine speed.
• If the cylinder engine speed values (Engine Speed Cylinder #1 to #6) displayed in the Data List do not change from an extremely high value, return to the Active Test menu screen, change "Check the Cylinder Compression" to "Start" and crank the engine again within 1 second.

NOTICE:

• Do not crank the engine continuously for 20 seconds or more.
• If it is necessary to crank the engine again after Check the Cylinder Compression has been changed to "Start" and the engine has been cranked once, press Exit to return to the Active Test menu screen. Then change Check the Cylinder Compression to "Start" and crank the engine.
• Use a fully-charged battery.

NOTICE:

• If the Active Test is changed to "Stop" while the engine is being cranked, the engine will start.
• When performing the Active Test, DTC P160400 (Startability Malfunction) may be stored.
• After performing the Active Test, make sure to check and clear DTCs.

HINT:

• If the value of Data List item "Engine Speed Cylinder" of a cylinder is higher than other cylinders, the cylinder may be malfunctioning.
• If the value of Data List item "Engine Speed Cylinder" is high for only one cylinder, compression loss is suspected.

HINT:

• Increase and decrease the fuel injection volume of the port injection and direct injection simultaneously and check the vehicle condition.
• Change the fuel injection volume between the minimum and maximum range of correction (e.g. -12.5% to 24.8%).
• When switching the injection method and performing the "D-4S (Injection Volume)" Active Test, switch from "Port" to "Direct".
• Do not switch from "Direct" to "Port". When performing the inspection more than once, after the Active Test ends, lightly race the engine, and then perform the inspection from "Port" again.
• If the display does not switch from "Port" even after lighting racing the engine, idle the engine for approximately 1 minute, and then lightly race the engine.

HINT:

• Interchange the ignition coil assembly and spark plug of the malfunctioning cylinder with those of a known good cylinder and check if the malfunctioning cylinder returns to normal.
• If the spark plug of the malfunctioning cylinder is abnormally wet with fuel even after the ignition coil assembly and spark plug are replaced, a leaking fuel injector assembly is suspected.

NOTICE:

• Make sure that the cloth or your fingers do not get caught in the valve.
• Make sure that foreign matter does not enter the throttle valve.
• Do not directly apply non-residue solvent to the throttle body with motor assembly or wash the throttle body with motor assembly. Cleaning solvent may leak into the motor from the shaft and cause problems such as rust or valve movement problems.
• If there is coating material on the edge of the valve, be careful not to remove it.

HINT:

• If the air fuel ratio learned value is corrected to the positive side for all operating ranges due to low fuel injector assembly injection volume, replace the fuel injector assemblies of all cylinders.
• Perform "Inspection After Repair" after replacing the fuel injector assembly.

  Click here

NOTICE:

• The air fuel ratio sensor has an output delay of a few seconds and the heated oxygen sensor has a maximum output delay of approximately 20 seconds.
• Read the output voltage immediately after warming up the air fuel ratio sensor and heated oxygen sensor to avoid an inaccurate reading due to a sensor cooling.

HINT:

• Increase and decrease the fuel injection volume of the port injection and direct injection simultaneously and check the vehicle condition.
• Change the fuel injection volume between the minimum and maximum range of correction (e.g. -12.5% to 24.8%).
• When switching the injection method and performing the "D-4S (Injection Volume)" Active Test, switch from "Port" to "Direct".
• Do not switch from "Direct" to "Port". When performing the inspection more than once, after the Active Test ends, lightly race the engine, and then perform the inspection from "Port" again.
• If the display does not switch from "Port" even after lighting racing the engine, idle the engine for approximately 1 minute, and then lightly race the engine.

HINT:

• If there is foreign matter in the intake system components, remove it before proceeding to the next step.
• If there is no foreign matter in the intake system components, check for foreign matter in the mass air flow meter sub-assembly. If there is foreign matter in the mass air flow meter sub-assembly, remove it.

• Engine mount deterioration
• Deposits in the intake manifold or on an intake valve
• Delay in fuel supply due to adherence of the fuel to the deposits

Drive Start Control

Engine Difficult to Start

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