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P0300 code

Tiny
BEV FRIEND
  • MEMBER
  • 2000 CHEVROLET MALIBU
  • 3.1L
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 68,000 MILES
I have been having off and on acceleration issues for weeks. More of a hesitation when accelerating, had power if pushed. Also around the same time the cruise control would kick off either with acceleration up a hill or if you hit a bump in the road. Recently had the check engine light on, came up with a P0300 code. Changed the spark plugs, wires and fuel filter. Almost feels worse now, is happening more often. In the past there was a very loud sound from under the engine like something fell out. Someone mentioned it may be the blow out plug for the catalytic converter. Other than that the gas mileage sucks, tried a gas additive, car has a slight leak in the gas line, but I doubt this is the issues (just water in the line.) Yesterday it clunked real hard twice like a transmission issue, not sure if that is the misfire or related to that over the engine. Help!
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Monday, July 25th, 2016 AT 1:25 PM

12 Replies

Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
P0300 is random misfire. Your cheapest option is to take to a mechanic and let him fix it due to you will be putting parts that may not be bad on the engine. It can be any sensor in engine as well as injectors or vacuum leak and basic engine problems.
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Monday, July 25th, 2016 AT 3:28 PM
Tiny
BEV FRIEND
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  • 7 POSTS
I have already taken it to a backyard mechanic who found the code on his hand held computer. The check engine light has gone off for a few days and flickered a little today but the car ran better than previously. What can a mechanic with a garage tell me differently than this guy's hand held?
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Monday, July 25th, 2016 AT 8:32 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
The professional can freeze frame it and run another program on it so he can check the sensors to see if they are working correctly. Because they can be or one of them may be the problem. Obviously the backyard guy did not do anything except put some parts on that were probably good to begin with along with him charging for labor.
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+1
Tuesday, July 26th, 2016 AT 5:30 AM
Tiny
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  • MEMBER
  • 7 POSTS
The other parts were needed regardless as the car was barely driven by a little old man (seriously) and nothing had been replaced probably in a decade. To note the car did need a fuel pump prior to my buying it and had about 64,000 miles I think on it at the time. Seemed like it should not have gone so soon but with the way it hesitates and going through gas so much could that cause a code or not? With the freeze frame, what other program would need to be run? I am low income and looking to sell this car soon which is why I went to someone who charges less to do the work. I would prefer he continue instead of paying up to $60.00 an hour plus parts. Thanks.
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Tuesday, July 26th, 2016 AT 6:06 AM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
They do freeze frame then a mode six which the scanner your backyard guy does not have plus because they deal with it everyday they know what the voltages should be on different sensors. With misfires that is the cheapest option. Well it is your choice if you decide to have backyard guy do it. A code will make your car get poor fuel mileage.
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Tuesday, July 26th, 2016 AT 6:13 AM
Tiny
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  • 7 POSTS
Okay, thank you. Then I guess it needs to have a regular mechanic then, thank you.
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Tuesday, July 26th, 2016 AT 12:41 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Just to add to this one, has the back pressure on the exhaust system been checked? Also might have a catalytic converter issue as well.
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Wednesday, July 27th, 2016 AT 12:39 PM
Tiny
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  • 7 POSTS
That was my initial thought, asked the backyard mechanic and he said no. Is the back pressure something he or I could check and how or only a licensed mechanic?
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Wednesday, July 27th, 2016 AT 1:27 PM
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
If you suspect back pressure, put a vacuum gauge on intake and take a reading at idle if 15" or below it could be.
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Wednesday, July 27th, 2016 AT 3:56 PM
Tiny
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Okay, thank you!
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Wednesday, July 27th, 2016 AT 4:47 PM
Tiny
SATURNTECH9
  • MECHANIC
  • 30,869 POSTS
Honestly I have tried the vacuum trick and it passed and I had a plugged cat on that car. So I never went back and ever used that trick again. You can test back pressure with a back pressure gauge they screw into o2 sensor hole. Exhaust shops can test it for you
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Wednesday, July 27th, 2016 AT 5:49 PM
Tiny
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Good to know :)
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Wednesday, July 27th, 2016 AT 6:15 PM

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