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1998 Chevy Blazer Engine running rough at idle

Tiny
DBRAB1207
  • MEMBER
  • 1998 CHEVROLET BLAZER
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 143,500 MILES
I can crank the vehicle and it runs, but it runs really rough at idle. I have changed the plugs, wires, MAF sensor, EGR valve, and all three O2 sensors. I did all this because when I put the code reader on the truck it was reading these as problem areas. I was hoping that these replacement parts would take care of the problem, but they haven't. The truck has started running a little better with each part I replace. I put the code reader on it today and am getting a P0300 code. This has come up each time I have changed a part and I keep getting different reading on my long term and short term fuel trim. As of right now it is reading Short Term Fuel Trim Bank 1-35.94%, Long Term Bank 1- -3.13%, Short Term Bank 2- -7.81%, and Long Term Bank 2- -3.13%. Is there anything other that I need to change and could my catalytic converter be affecting the readings?
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Monday, December 22nd, 2008 AT 7:51 PM

1 Reply

Tiny
BRIAN 1
  • MECHANIC
  • 1,030 POSTS
The readings won't affect the cat, but the p0300 missfire will. After awhile the missfire will affect the cat because it's dumping raw fuel into the exhaust and will plug the cat. For there were 2 major problems with the 4.3 engines. The injector poppet valves sticking causeing a missfire and the fuel pressure regulator leaking gas. You need to check these, replacing parts will not help until you figure out what is wrong. Post back with what you find and will advise from there.
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Monday, December 22nd, 2008 AT 10:31 PM

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