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  1. #1

    Default Multiple engine codes on 04 Colorado: PO300 and PO506-running rough

    Hi Guys: First Post: I have had an engine code for a few months: PO300 and PO506....the probable causes are listed as:
    vacuum leak, dirty throttle body, IAC motor defective, poor connection to IAC valve, injector fault, high or low fuel pressure. It's idling rough and seems to be getting poor mileage. So many places to start that it's a little overwhelming. Thanks in advance for any suggestions.
    Novice, but trying hard to get better at DIY

    Tom in Florida

    2004 Colorado 5 cylinder,,,,110,000 miles

  2. #2


    Welcome to the club!!

    I would defiantly try to clean the throttle body, as someone else on the forum had the same issue. I don't remember the thread so I cannot provide a link, sorry.

    2009 Chevy Silverado!

    Blacked out tail lights + 3rd brake light
    l Tint: 35% front windows and Limo on the rest l Hard wired Valentine One radar detector l Pirelli Scorpion Ice & Snow tires with GM CK375 wheels l Hand welded receiver hitch l HID lighting l SMD lighting l Blacked out front and rear emblems l Cherry Bomb Extreme exhaust dumped l 2 Kenwood 12's powered by a Kenwood amp w/ an Base control l

    2007 Chevy Tahoe LTZ---2012 Chevy Cruze

    "Let's just agree that a perfect truck is hard to find, and we'll drive the Silverado till we find it." - Car and Driver

  3. #3


    Welcome to the club!

    2011 GMC SIERRA CREW CAB 2WD W/5.3

    Convenience Package
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    You can't get away from the STORM!

  4. #4


    We are the Borg. Lift your vehicle and surrender your keys. We will add your biological and technological distinctiveness to our own. Resistance is futile. Erm, I mean ... welcome to GM Truck Club! I agree with TTR, clean the throttle body first, as it is inexpensive (need to buy cleaner) and doesn't take long. Maybe clean the mass airflow sensor while you're at it...

  5. #5


    Quote Originally Posted by SurrealOne View Post
    We are the Borg. Lift your vehicle and surrender your keys. We will add your biological and technological distinctiveness to our own. Resistance is futile. Erm, I mean ... welcome to GM Truck Club! I agree with TTR, clean the throttle body first, as it is inexpensive (need to buy cleaner) and doesn't take long. Maybe clean the mass airflow sensor while you're at it...
    Gonna add on to this by saying to clean your MAF sensor with a fast dry electronics cleaner. NOT ELECTRIC PART CLEANER... the electric parts cleaner leaves a nasty residue and as important as a MAF is to the computer.. you dont want that. Most likely you wont find the electronics cleaner at your local parts store, but rather a local electrical parts supplier.

    If that doesn't work (not sure how mechanically inclined you are but,) you may try pulling the IAC valve off and checking to see if its gummed up or anything as I've seen that a few times myself.

    I've also seen the PCV valve cause funky codes to be shown as well.

    Or if all else fails.. pull the motor and replace it with a 5.3

    Welcome to the forum! Keep us posted on what ya find bud!

    "If you're not living life on the edge, You're taking up too much space"

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  6. #6


    Welcome to the club Tom, it's good to have you with us.

    2002 Chevrolet Silverado Extended Cab SportSide: See Mods in My Garage

  7. #7

    mfleetwood's Avatar
    Join Date
    Jul 2010
    Denver, CO
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    ****Thread Moved****

    Welcome to the Club!!! See if the information below is helpful.

    Symptoms may include:

    • the engine may be harder to start
    • the engine may stumble / stumble, and/or hesitate
    • other symptoms may also be present


    A code P0300 may mean that one or more of the following has happened:

    • Faulty spark plugs or wires
    • Faulty coil (pack)
    • Faulty oxygen sensor(s)
    • Faulty fuel injector(s)
    • Burned exhaust valve
    • Faulty catalytic converter(s)
    • Stuck/blocked EGR valve / passages
    • Faulty camshaft position sensor
    • Defective computer

    Possible Solutions

    If there are no symptoms, the simplest thing to do is to reset the code and see if it comes back.
    If there are symptoms such as the engine is stumbling or hesitating, check all wiring and connectors that lead to the cylinders (i.e. spark plugs). Depending on how long the ignition components have been in the car, it may be a good idea to replace them as part of your regular maintenance schedule. Check spark plugs, sparkplug wires, distributor cap, and rotor (if applicable). Otherwise, check the coils (a.k.a. coil packs). In some cases, the catalytic converter has gone bad. If you smell rotten eggs in the exhaust, your cat converter needs to be replaced. In other cases the problems were faulty fuel injectors.
    Random misfires that jump around from one cylinder to another (read: P030x codes) also will set a P0300 code. The underlying cause is often a lean fuel condition, which may be due to a vacuum leak in the intake manifold or unmetered air getting past the airflow sensor, or an EGR valve that is stuck open.

    Possible causes
    - Dirty throttle body
    - Electric throttle control actuator misadjusted or damaged
    - Faulty Electric throttle control actuator
    - Intake air leak
    - Poor electrical connection to the Intake Air Control (IAC) valve Help with this

    Tech notes
    If there are no intake leaks, clean throttle body, adjust engine idle and erase engine code. If the code comes back you may have to replaced the Electric Throttle Control Actuator (Motor) to repair the problem.
    Service Support Bulletin:

    When is the code detected?

    The idle speed is less than the target idle speed by 100 rpm or more.

    - Engine Light ON (or Service Engine Soon Warning Light)
    - Engine hard to start
    - Rough or erratic idle speed

    P0506 GMC Description
    The Engine Control Module (ECM) controls the engine idle speed to a specified level through the fine adjustment of the air, which is let into the intake manifold, by operating the electric throttle control actuator. The operating of the throttle valve is varied to allow for optimum control of the engine idling speed. The ECMcalculates the actual engine speed from signals of crankshaft position sensor (POS) and camshaft position sensor.

    The ECM controls the electric throttle control actuator so that the engine speed coincides with the target value memorized in the ECM. The target engine speed is the lowest speed at which the engine can operate steadily. The optimum value stored in the ECM is determined by taking into consideration various engine conditions, such as during warming up, deceleration, and engine load (air conditioner, power steering and cooling fan operation, etc.)

    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

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  8. #8


    Thank you guys for your generous tips on the engine codes. The cleaning of the throttle and the MAF worked wonders. As I am a novice, it was pretty gratifying to not have to take it in and get gouged.


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