P0300 means it has detected a misfire.
P0171 refers to lean fuel mixture.
I have included some info for you that explains it in detail. Basically it sounds like there is a vacuum leak in the engine area somewhere,,,the tricky part is finding it. I suggest looking around under the hood for and loose or disconnected vac hoses. You can also take a can of carb spray and lightly spray around different areas on the engine,,,wherever there are vac hoses,,,if you come across an area to where the idle increases, there is a vac leak. If nothing found,,,unfortunatly it will have to be hooked up to a factory level scan tool to isolate the culprit.
If you have any further questions, please feel free to reply.
If not, please click on ACCEPT Thanks for asking!
According to my database its classified as a LS2..
Best of luck my friend!
I just double checked and yes the LS2 has the alum block, used mainly in the corvette but could be special ordered for the Denali,,,sorry for the confusion.