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Codes P0300 and P0302, misfiring, RPM's fluctuations on cold start

Tiny
DRFIROJTADAVI
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  • 33 POSTS
Today check engine light came on and having code p300 and p304. As previously it was P302 constantly for last 6 months.
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Wednesday, January 6th, 2021 AT 7:08 PM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Yes, did you service the throttle bore? also we should check for a vacuum leak. this guide can help:

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

if no leak I would get a new MAF sensor as well.
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Thursday, January 7th, 2021 AT 11:25 AM
Tiny
DRFIROJTADAVI
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I will check vacuum leaks again. I have replaced the throttle body and MAF sensor before this problem approximately 2 months before still do I need to replace it?
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Thursday, January 7th, 2021 AT 11:44 AM
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
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Not really, I am leaning toward the vacuum leak.
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Thursday, January 7th, 2021 AT 12:10 PM
Tiny
DRFIROJTADAVI
  • MEMBER
  • 33 POSTS
Okay, I will let you know.
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Thursday, January 7th, 2021 AT 12:23 PM
Tiny
DRFIROJTADAVI
  • MEMBER
  • 33 POSTS
At cold start when misfiring and RPM fluctuations occurring the advance timing for cylinder number 1 is negative (retarded) 13-15 degrees, when the advanced timing becomes positive around 5-10 degrees the rpm stabilise. Is it normal or its having issues of ignition timing?
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Friday, February 5th, 2021 AT 10:50 AM

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