Rough Idling [01/2019 - 11/2022]: Description

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.

1. 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.

   1. 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

   2. 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	Target Air-Fuel Ratio AF Lambda B1S1 Short FT B1S1 Long FT B1S1 Total FT #1 Fuel System Status #1 A/F Learn Value Idle #1 A/F Learn Value Low #1 A/F Learn Value Mid1 #1 A/F Learn Value Mid2 #1 A/F Learn Value High #1
      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

   3. Intake and exhaust systems
      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 Flow ISC Feedback Value ISC Learning Value Electric Load Feedback Val Air Conditioner FB Val Eng Stall Control FB Flow

      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 B1S1 O2S B1S2 Fuel System Status #1

   4. 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
      Data List	Compression Leakage Count Rough Idle Status Plural Cylinders Rough Idle Rough Idle #1 Rough Idle #2 Rough Idle #3 Rough Idle #4
      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.

   5. CVT system
      CVT
      
      

      Main cause of malfunction	Shift solenoid valve SLU stuck on
      Symptom	Engine speed drops or rough idle occurs due to delay in lock-up OFF operation
      Data List	Engine Speed SPD (NT) Shift SW Status (D Range)
      HINT:  If the rough idling occurs during neutral control under idling, CVT system is suspected.

2. 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.

   • Engine Speed
   • MAF
   • ISC Flow
   • ISC Feedback Value
   • ISC Learning Value
   • Electric Load Feedback Val
   • Air Conditioner FB Val
   • Neutral Control
   • Eng Stall Control FB Flow
   • Target Air-Fuel Ratio
   • AF Lambda B1S1
   • AFS Voltage B1S1
   • O2S B1S2
   • Short FT B1S1
   • Long FT B1S1
   • Total FT #1
   • Fuel System Status #1
   • Cylinder #1 Misfire Count
   • Cylinder #2 Misfire Count
   • Cylinder #3 Misfire Count
   • Cylinder #4 Misfire Count
   • Compression Leakage Count
   • Rough Idle Status
   • Plural Cylinders Rough Idle
   • Rough Idle #1
   • Rough Idle #2
   • Rough Idle #3
   • Rough Idle #4
   • A/F Learn Value Idle #1
   • A/F Learn Value Low #1
   • A/F Learn Value Mid1 #1
   • A/F Learn Value Mid2 #1
   • A/F Learn Value High #1
   • SPD (NT)
   • Shift SW Status (D Range)