Rough Idling [12/2019 - ]: Description

HINT: 

• If any DTCs are output, perform troubleshooting for the DTCs first.
• Try to reproduce the conditions present when the malfunction occurred.
• Using the GTS, 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	Misfire Count Cylinder #1 to #4
      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	Misfire Count Cylinder #1 to #4

   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	Short FT B1S1 Long FT B1S1 Total FT Bank 1 Fuel System Status Bank 1 Target Air-Fuel Ratio A/F (O2) Lambda Sensor B1S1 A/F Learn Value Idle (Port) Bank 1 A/F Learn Value Low (Port) Bank 1 A/F Learn Value Mid No. 1 (Port) Bank 1 A/F Learn Value Mid No. 2 (Port) Bank 1 A/F Learn Value High (Port) Bank 1 A/F Learn Value Idle Bank 1 A/F Learn Value Low Bank 1 A/F Learn Value Mid No. 1 Bank 1 A/F Learn Value Mid No. 2 Bank 1 A/F Learn Value High Bank 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
      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 Valve Position No. 1 Normally, Actual EGR Position = Target EGR Valve Position No. 1 +/-5% (fully closed: 0%, fully open: 100%) When the ignition switch is turned to ON, 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	Mass Air Flow Sensor
      HINT:  If the value of the Data List item "Mass Air Flow Sensor" 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	Engine Stall Control F/B Flow ISC Learning Value

      AIR FUEL RATIO SENSOR (SENSOR 1), AIR FUEL RATIO SENSOR (SENSOR 2)
      
      

      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	A/F (O2) Sensor Current B1S1 A/F (O2) Sensor Current B1S2 Fuel System Status Bank 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
      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 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.

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.

   • Mass Air Flow Sensor
   • Engine Stall Control F/B Flow
   • Target Fuel Pressure (High)
   • Target Fuel Pressure (Low) / Target Fuel Pressure 2
   • Fuel Pressure (High)
   • Fuel Pressure (Low) / Fuel Pressure 2
   • Fuel Pump Control Duty Ratio
   • High Pressure Fuel Pump Duty Ratio (D4)
   • High Pressure Fuel Pump Discharge Rate
   • Target Air-Fuel Ratio
   • A/F (O2) Sensor Current B1S1
   • A/F (O2) Sensor Current B1S2
   • Short FT B1S1
   • Long FT B1S1
   • Total FT Bank 1
   • Fuel System Status Bank 1
   • A/F Learn Value Idle (Port) Bank 1
   • A/F Learn Value Low (Port) Bank 1
   • A/F Learn Value Mid No. 1 (Port) Bank 1
   • A/F Learn Value Mid No. 2 (Port) Bank 1
   • A/F Learn Value High (Port) Bank 1
   • A/F Learn Value Idle Bank 1
   • A/F Learn Value Low Bank 1
   • A/F Learn Value Mid No. 1 Bank 1
   • A/F Learn Value Mid No. 2 Bank 1
   • A/F Learn Value High Bank 1
   • Target EGR Valve Position No. 1
   • EGR Step Position
   • Misfire Count Cylinder #1 to #4
   • ISC Learning Value