I'am new to this so bear with me. Have a 97 riviera 145k miles .Pulling po300 code, can anyone tell me what it could be??

A p0300 code is an engine misfire detected

A tech 2 could tell you which cylinders are misfiring but if you dont have access to that i personally would start with new spark plugs and wires.

Hi Mike, I'am trying to figure out what would cause the missfire?

Give this a shot and see what happens.

https://www.gmforum.com/obd-ii-troub...0/#post1390843

Ronn, do you have a scanner? Without being able to monitor the engine systems you are in the dark. Spark plugs and wires are always a good start especially if you don't know how old they are. Spend a few extra bucks on better wires. They make a big difference on these cars.

Most of the misfire issues we see on the forum are resolved with new plugs and wires. If they have not been changed in a while, or you don't know the history, you should start there.