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Misfire - rough idle

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
The black soot sounds like it is running rich. If the mil is on, there should be codes. This guide can help you get the codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

Please run down this guide and report back.
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Monday, November 16th, 2020 AT 10:42 AM (Merged)
Tiny
PETELOMELI
  • MEMBER
  • 1 POST
  • 2004 CHEVROLET SILVERADO
  • V8
  • 2WD
  • AUTOMATIC
  • 86,000 MILES
Engine idles rough when truck stopped at intersections and decrease in mileage
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Monday, November 16th, 2020 AT 10:42 AM (Merged)
Tiny
F4I_GUY
  • MECHANIC
  • 3,302 POSTS
Scan the PCM for any pending codes or DTC's.

If nothing is found, then I would assume you have a bit of a mis-fire. When's the last time you had a tune-up done?
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Monday, November 16th, 2020 AT 10:42 AM (Merged)
Tiny
SPIELMAN54
  • MEMBER
  • 4 POSTS
  • 2004 CHEVROLET SILVERADO
  • V8
  • 4WD
  • AUTOMATIC
  • 53,000 MILES
My truck keeps running with a rough idle and the engine light goes on. 1st was about a 2 months ago, took it in and mechanic said it might be bad gas (codes I believe misfires on 2, 4, 6, 8). They poured some 3M gas additive in the tank and the idle cleared up and light went off. About a month later and 2 tanks of gas (different stations) the problem came back. Codes said something like 'gas lean warning' This time they gave me a fuel injector cleaning, and ran that same 3m stuff through the injectors. That lasted a week and again I am back to rough idle. They have mentioned that it may be bad injectors, I don't want to spend that money unless I know it is the problem and will fix it. Any ideas?
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Monday, November 16th, 2020 AT 10:43 AM (Merged)
Tiny
DENNYP
  • MECHANIC
  • 1,824 POSTS
Post the codes for us. It could be water in the fuel rail.
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Monday, November 16th, 2020 AT 10:43 AM (Merged)
Tiny
SPIELMAN54
  • MEMBER
  • 4 POSTS
The codes are P0174 and P0300
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Monday, November 16th, 2020 AT 10:43 AM (Merged)
Tiny
MASTERTECHTIM
  • MECHANIC
  • 4,749 POSTS
Check the fuel pressure regulator on the fuel rail. Unplug the vacuum hose and see if fuel comes out. With those codes its got to be the regulator.
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Monday, November 16th, 2020 AT 10:43 AM (Merged)
Tiny
SPIELMAN54
  • MEMBER
  • 4 POSTS
Thanks for the advice. Is this something easy enough for me to do? I've done brakes, oil, plugs and wires, but thats about it. Where would I start?
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Monday, November 16th, 2020 AT 10:43 AM (Merged)
Tiny
SPIELMAN54
  • MEMBER
  • 4 POSTS
This keeps getting better, I put some seafoam in a new full tank and ran it a while on another suggestion and now the codes are: P0135, P0141, P0151, P0155, P0161, P0174, P1153, P0300

Does this help?
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Monday, November 16th, 2020 AT 10:44 AM (Merged)
Tiny
DENNYP
  • MECHANIC
  • 1,824 POSTS
Check your O2 sensor fuses under the hood. O2A and O2B, they are 15 amp fuses.
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Monday, November 16th, 2020 AT 10:44 AM (Merged)
Tiny
DENNYP
  • MECHANIC
  • 1,824 POSTS
Check your intake gaskets for any leaks when the engine is still cold. Also, are you running E-85 fuel in the tank?
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Monday, November 16th, 2020 AT 10:44 AM (Merged)

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