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Malibu 2008 2.4 has PO300 and PO171 codes. Installed new spark plugs, fuel injectors, and upstream CO2 sensor. Car does not hold idle and the engine stumbles unless you maintain 2500+ rpms then engine seems to run ok. Fuel pressure is 60 psi. Spark from coils is evident with spark tester. I can't find any evidence of a vacuum leak. Would upgrading my simple obdII tester give me more information then the PO codes? Any suggestions on next diagnostic steps will be appreciated. Thanks.
 

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I would clean the throttle body first along with the MAF. P0300 is a general miss fire code and can result from other codes. If you have a cold air intake kit on it take it off.
A better scan tool will read ECT temps and MAF sensor inputs like the IAT. A great scan tool is a good investment and needed when doing your own repairs now and into the future.
|What are the Possible Causes of the P0171 CHEVROLET Code?
  • Dirty or Restricted Air Filter
  • Dirty or Faulty Mass Air Flow (MAF) Sensor
  • Intake Air Leaks
  • Exhaust Gas Leaks
  • Fuel Contamination
  • Faulty or Clogged Fuel Injectors
  • Faulty Front Heated Oxygen Sensor
  • Ignition Misfiring
  • Low Fuel Pressure
  • Positive Crankcase Ventilation (PCV) Hose Leaks
  • Engine Control Temperature (ECT) inaccurate readings
 
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