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JOHN aka Eauto
JOHN aka Eauto, The Car Guy
Category: Chevy
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Experience:  ase tech
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2004 chevy malibu: 2.2L..spark plugs..The car runs..misfiring

Customer Question

2004 chevy malibu 2.2L I have a code P0300 so I changed the spark plugs. The car runs well and is driveable for about 2 miles then it starts misfiring and stumbles. What else could it be?
Submitted: 7 years ago.
Category: Chevy
Expert:  JOHN aka Eauto replied 7 years ago.
Is the po 300 the only code present?
Customer: replied 7 years ago.
Expert:  JOHN aka Eauto replied 7 years ago.

DTC P0300

The powertrain control module (PCM) uses information from the crankshaft position (CKP) sensor and the ignition control (IC) module in order to determine when an engine misfire is occurring. By monitoring variations in the crankshaft rotation speed for each cylinder, the PCM is able to detect individual misfire events. A misfire rate that is high enough can cause the 3-way catalytic converter (TWC) to overheat under certain driving conditions. The malfunction indicator lamp (MIL) will flash ON and OFF when the conditions for TWC overheating are present. If the PCM detects a misfire rate sufficient to cause emission levels to exceed mandated standards, DTC P0300 will set.


  • DTCs P0105, P0107, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0131, P0132, P0133, P0134, P0171, P0172, P0336, P0340, P0341, P0502, P0503, P0506, P0507, P0601, P0742, P1133, P1621 are not set.
  • The engine speed is between 469-6,400 RPM.
  • The ignition voltage is between 9-17 volts.
  • The engine coolant temperature (ECT) is between -7 and +123°C (20-254°F).
  • The engine has been running for more than 5 seconds.
  • The throttle position (TP) has not increased more than 8 percent in 1 second.
  • The TP has not decreased more than 1.5 percent in 1 second.

The PCM is detecting a crankshaft rotation speed variation indicating a misfire sufficient to cause emission levels to exceed mandated standards.


  • The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails.
  • The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records.


  • The control module turns OFF the malfunction indicator lamp (MIL) after 3 consecutive ignition cycles that the diagnostic runs and does not fail.
  • A current DTC, Last Test Failed, clears when the diagnostic runs and passes.
  • A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic.
  • Clear the MIL and the DTC with a scan tool.
TEST DESCRIPTION graphicgraphicgraphic
Customer: replied 7 years ago.

I have a OBD II AutoScanner so what is my next step? Do I follow your test discription step by step?

Expert:  JOHN aka Eauto replied 7 years ago.
Thats is the chevy test procedure you will need to follow the flow chart step by step to solve the issue.....
Customer: replied 7 years ago.
OK. I don't have the car home with me because it started to misfire when my son reached his friends home. He will leave it there over night then bring it home in the morning. At that time I will attempt to follow the flow chart. Will I be able to reach you for anymore questions if I get stuck?
Expert:  JOHN aka Eauto replied 7 years ago.
Yes just reply to this i will help
JOHN aka Eauto and 5 other Chevy Specialists are ready to help you
Customer: replied 7 years ago.

OK. so i changed the spark plugs, changed the control modulator, and changed the catalytic converter but it still misfires when I start to slow down and the car goes into idle. The check engine light starts blinking then stops when it stops misfiring at a higher rpm. Then when I slow down at the traffic light it starts again. I did not check the fuel injectors. What should I do next?


Expert:  JOHN aka Eauto replied 7 years ago.
have you checked fuel pressure?
Customer: replied 7 years ago.
Expert:  JOHN aka Eauto replied 7 years ago.
i would verify fuel pressure weak fuel pump can cause a miss
Customer: replied 7 years ago.
should I also check the egr valve and if so do you know were its located?
Expert:  JOHN aka Eauto replied 7 years ago.
dont think its a egr issue i would think more like a fuel pump or injector issue
Customer: replied 7 years ago.
John thanks, XXXXX XXXXX I will try checking the pressure. Any advice on how to do it?
Expert:  JOHN aka Eauto replied 7 years ago.

with a fuel pressure gauge available at most part stores and it threads into the test port on the fuel rail


Customer: replied 7 years ago.
The pressure was checked and turning the key is 50psi and with the car on 57psi.
Expert:  JOHN aka Eauto replied 7 years ago.
its got to be in the injectors or a clogged fuel rail i woulod look into the injectors a little closer
Customer: replied 7 years ago.
Thanks I will continue tomorrow and let you know how it goes.
Expert:  JOHN aka Eauto replied 7 years ago.
Customer: replied 7 years ago.
So now i cleaned the fuel rail and the plugs and when I started the car it ran good for a little while so I took it for a run and it felt like i needed to gun it to stop the fluttering. It seemed to work so I parked it and went to bed. In the morning when I started it, it started misfireing again so I gave up and took it into a repair shop and they changed the fuel coil and as I drove it away it had power like it used too but was shakey at idiol. Then the 300 code came up again. Now this morning the car kicks over but does not start. I rented a fuel pressure tester once again and I still have good presure. What do I do now?
Expert:  JOHN aka Eauto replied 7 years ago.
are you getting spark and injector pulse?

We will have to pinpoint what the engine is missing.





All three of these are tested when the engine is being cranked over. There are two way of checking for fuel. Fuel pressure and fuel trigger. Both are very important and must be present for the car to start. Fuel pressure is self explanatory. You just hook up the gage and see what the reading is. Fuel trigger is check with a noid light. The injector gets unplugged and the noid light gets plugged in to the injector clip. With the engine cranking over, this light must blink. This is the signal to the injectors from the computer. You can have all the fuel pressure in the world, but it wont matter if the injector is not pulsing gas into the cylinder like it should! Compression tester, spark tester, fuel pressure gage and noid light are all accessible at your local auto store. All three tests play a very important part in diagnosing a no start condition.

Customer: replied 7 years ago.
Thanks, I'll check that tomorrow and get back with you.

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