I have a 2003 5.3 it just started missing, and throwing a code po300, it has 96,000 miles on it could it be time for plugs or do I have other problems? It does it the most on startup whether hot or cold.

Thanks

 

plugs and wires will probably fix it if you are not having any running problems. otherwise it could be fuel related or plugged cats.

 

Yea, do the basics first, plugs, wires, fuel filter, etc. Speaking of fuel, check and make sure that your fuel pressure regulator isn't leaking. Pull the hose off of the fp reg and check for the presence of fuel, if fuel drips out or there is a strong gas odor, the fp reg is leaking and should be replaced. (the fp reg is located in the center of the driver's side fuel rail)

Clogged cats will usually misfire under load, and the engine may not rev up past 4k if they were clogged or breaking down and blocking exhaust flow.

 

No cats, I will check hose today. Thanks

 

Now I get to show my ignorance, the hose you are talking about, is it the vacuum hose?

 

Yep, it's a thin vacuum hose that goes to a round metal item in the center of the driver's side fuel rail

 

No gas smell or presence, I will try plugs and wires.
Thanks