Trouble cylinder 1

[Carmen Aguirre]

my 2004 Avalanche has been throwing me P0301 code for a while now I cannot figure it out I replaced the spark plugs wires,coil. injector, plugs, is Jewel the trouble Cold Steel returns it idles fine when it starts but after about 30 seconds it goes to rough idle and it feels like it wants to die. I've tried the injector cleaner up in the gas Octane and I still cannot figure it out can you help me this messages for wrencher, as I saw a previous post that he was pretty knowledgeable or anyone else that could lead me in the right direction to fix my issue thank you

[Jsdirt]

Could be anything from a big intake air leak, to broken valve springs and low compression. You can spray water around the intake gasket surface to rule out an air leak. 

 

Need to do a compression and leak down test to rule compression-related issues out.