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Code PO300, random or multiple cylinder misfire codes

Tiny
TEDDY CALHOUN
  • MEMBER
  • 1999 VOLVO S70
  • 2.4L
  • 5 CYL
  • 2WD
  • MANUAL
  • 140,000 MILES
The check engine light comes on and the car starts shaking and jerking around the engine block. We've tried looking at and cleaning/replacing spark plugs and engine coils. It seemed okay for a day but then it started all over again. Trying not to go to the mechanic because it really isn't worth the money. We're going to sell it for parts but would like to be able to drive it around town while looking for a replacement vehicle.
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Sunday, April 24th, 2022 AT 8:20 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,644 POSTS
Hi,

By chance, is the P0300 the only code you get? Also, is this an intermittent issue or does it start when the engine is started and not stop until it's turned off?

There are several different things that can cause this type of issue. For example, it could be a fuel pressure-related issue. an emissions-related issue, and so on.

If possible, I need you to check for two things to get started. First, confirm there are no engine vacuum leaks. Here is a link that explains how that is done:

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

If that all checks good and there are no other codes, check fuel pressure. Here is a link that explains how it's done:

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

Let me know as much as you can. Also, pay attention to when it does this if there is dark smoke from the exhaust or any odd sounds or odors.

Let me know.

Joe
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Sunday, April 24th, 2022 AT 7:27 PM
Tiny
TEDDY CALHOUN
  • MEMBER
  • 3 POSTS
Hi Joe,

Yes, this is the only code we get, and it happens whenever we start the car and get going down the road. If we're just sitting in the driveway or the garage, the shaking doesn't happen. It's only after we're accelerating down the road. The car is actually with my daughter away at uni but I'm heading that way today to double check her work, so I'll be pulling out all the plugs and coils and replacing any that haven't already been replaced. She's already cleaned them, so I'll just be giving it another eye before moving on to your suggestions.

Ted
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Monday, April 25th, 2022 AT 5:18 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,644 POSTS
Hi,

If the plugs are used, I never had much luck cleaning them. You may want to replace them. However, since it is a random misfire, it's likely being caused by something different.

Regardless, let me know what I can do to help.

Joe
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Monday, April 25th, 2022 AT 5:46 PM
Tiny
TEDDY CALHOUN
  • MEMBER
  • 3 POSTS
Hi Joe,

We ended up replacing all the spark plugs and coils that hadn't already been replaced and that seems to have done the trick. We've driven it around 12 miles and no codes have returned, and the engine feels and sounds wonderful! I really appreciate all of your advice.

Best,

Ted
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Thursday, April 28th, 2022 AT 11:20 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,644 POSTS
Hi,

You are very welcome. I'm glad to know it helped, so thank you for the update.

It's funny when I think back. Many years ago, there was a small sandblaster that was used to clean spark plugs, and it would actually work. Anymore, sparkplugs are designed differently, and cleaning oftentimes doesn't help.

Regardless, thank you for the update, and please feel free to come back anytime in the future. You are always welcome here.

Take good care of yourself,

Joe
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Thursday, April 28th, 2022 AT 6:21 PM

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