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2003 Chevy Impala Ramdom misfire code 300

Tiny
WILIERMDB
  • MEMBER
  • 2003 CHEVROLET IMPALA
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 165,000 MILES
My '03 Impala (3.4L) has a random misfire code 300 and after replacing simple things it's still there. Replaced the fuel filter, air filter, PCV, plugs a year ago and wires last week.

I did find a rubber vacuum line leading to the PCV that was dried and cracked so I replaced that as well.

I guess my next step is to have a diagnostic test run but are there any tips you can provide as to what I should check next?

I've read about possible coil failure and fuel injectors/fuel pump issues. The car mainly misses at idle and it still gets good mileage at around 28 mpg on the highway averaging 70 mph for 450 miles on a trip I take every 8 weeks.

Thank you for any info you can provide.
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Sunday, February 21st, 2010 AT 8:34 AM

1 Reply

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Engine running rough or misfiring can be cause by the following:
1. Defective spark plug.
2. Inadequate spark/coil, defective spark plug wire.
3. Lack of compression
4. False air leakage.
5. Faulty fuel injectors.
6. Insufficient fuel pressure.
7. Contaminated fuel.
8. EGR valve that is leaking.
9. Oxygen sensors.
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Tuesday, February 23rd, 2010 AT 5:07 AM

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