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P0300 misfire

Tiny
GREGOPPOLD
  • MEMBER
  • 2003 MITSUBISHI MONTERO
Engine Mechanical problem 6 cyl All Wheel Drive Automatic 121000 miles

Montero Sport

Got this code a month ago and was told that the valve cover gasket was leaking and oil was getting down into the spark plugs. Had them replace plugs, wires, and gasket. Couple of days later the same code came up again. They put on their machine and drove it. Found the mass air flow was running at 60-70 and would drop to 40 (cfm I'm guessing). They changed that out but still did the same thing. They don't know what else to do so they told me to take it to the dealer. If anyone has come across this I would appreciate knowing.
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Sunday, January 17th, 2010 AT 3:44 PM

3 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Hello,

I dirty throttle body can cause the P0300 codes the computer picks up the misfire at idle. Here is a guide to help you fix the problem.

https://www.2carpros.com/articles/throttle-actuator-service

Sometimes points to false air/vacuum leaks and contaminated fuel, low fuel pressure, or even bad fuel.

https://www.2carpros.com/articles/how-to-check-fuel-system-pressure-and-regulator

and

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Please let us know what you find. We are interested to see what it is.

Cheers
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Sunday, January 17th, 2010 AT 3:55 PM
Tiny
CGHAWKINS
  • MEMBER
  • 5 POSTS
Mine is most noted at acceleration in overdrive. I am reading a lot of what I have thought it may be. I would like to know on average what the most common successful repair has been?
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Wednesday, May 23rd, 2018 AT 4:49 PM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,170 POSTS
Hi and thanks for using 2CarPros. Com It is hard to identify the most common cause of a P0300 because it is a random issue which can be caused by many different things. I agree with the aforementioned post from RAZMATAZ. He truly is indicating where I would start considering you already replaced the plugs and wires. Additionally, a weak coil, fuel pressure, camshaft or crankshaft sensor, a faulty injector, low cylinder compression, a worn timing belt or chain can cause it. You have already done what I would consider the most common reason.

If your mechanic has a really good scanner, he can actually identify which cylinders are randomly misfiring. You may want to ask if that is something he can do.

Let us know.
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Friday, May 25th, 2018 AT 7:56 PM

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