P0300 Rough Idle ideas? 2004 Z71 5.3

Discussion in 'Chevy Silverado Forum (GMC Sierra)' started by afireinside, Jul 21, 2013.

  1. afireinside

    afireinside Member

    Ok as I posted last week I bought a 216k Mile 2004 5.3L Z71.

    I knew the cig lighter dident work (dident really care) but the truck was idleing slightly rough this I also knew, but their was no CEL. Running it today a CEL came on, put my basic reader on and no power, goggled and found that a blown cig fuse can cause no power to the reader connection and it worked, ran it and got a p0300.

    Now the previous original owner "thinks" he had half or all the plugs changed at about 150k when he had a cracked head replaced but not sure. I have that "need a tune up smell" from the exhaust not completely rich smelling just that incomplete combustion smell. Air filter is clean, I just cleaned MAF nothing.

    So my first step is plugs I ordered NGK IZTR5B11 Laser Iridium That are pre gapped .40. Should I use these? Return and get AC Delco Platinum? Iridium? Should I go with wires or see if plugs?

    Other things I have read clean the flapper on the TB (wifes Mazda 3 would run rough after pulling battery due to carbon build up) and pull and clean or replace IAC Valve.

    Any other quick cheap fixes before I get too deep into digging?

    - - - Updated - - -

    Scratch that put the NGKs In and AC Delco 9748HH wires I got from Advanced Auto and all is well running great under throttle and idle is butter smooth.

    Stock plugs were the worst I have ever seen! They look every bit of 216k miles.........

    - - - Updated - - -

    ALSO cleaned TB while I was their
  2. ChevyBoy2009

    ChevyBoy2009 Rockstar 4 Years 500 Posts

  3. ridick_bowen

    ridick_bowen Rockstar 100 Posts

    you can do the whole seafoam thing and see if that helps any.

    Have you changed the fuel filter yet?
  4. stchman

    stchman Active Member 2 Years 1000 Posts

    I am amazed that spark plugs can actually go 200K+ miles. I would have bought the same brand and installed those. You might want to run a can of fuel injector cleaner in the gas tank.

    IMO, the steps you do when buying a used vehicle:

    Change rotor and distributor cap(if equipped).
    Change plugs, and if the vehicle has high mileage, change the wires.
    Change oil and filter.
    Lube job(if you can).
    Change transmission fluid.
    Change differential and transfer case fluid if equipped.
    Coolant system flush.
    Change air filter(K&N).
    Change serpentine belt.
    Change brake fluid.
    Change fuel filter.
    Run a bottle of fuel injector cleaner in the fuel tank(gas engines).
    Get AC refrigerant levels checked.
    Change cabin air filter.
    Clean throttle body.
    Inspect tires for wear and have alignment checked.
    Change power steering fluid.
    Inspect rubber hoses for possible leaks.

    I know this seems like a lot, but unless I knew the previous owner and was sure they stayed on top of the required maintenance, I would feel better having these things done.
  5. j cat

    j cat Epic Member 5+ Years 1000 Posts

    I would use the ac delco irridium plugs. you do not adjust the gap. if you do you will damage the small tip. if the gap looks off the plug is defective !

    before replacing any plug wires measure the resistance. many new wires are defective with POOR quality control.

Share This Page

Newest Gallery Photos