1997 Buick LeSabre

I would look at the p1406 first that code can cause the code P0300 if the egr valve is sticking open it can cause a vacuum leak causing the P0300 random miss fire code.I would start by removing the egr valve turn it upside down take a small screw driver you will see the spring loaded pintle start pushing it down see if it's stuck at first when pushing it down.Then slowly bottom it out then slowly release it and see if it sticks closed or open.

Thanks. I took it off and there was some carbon built up on it. Probably going to replace it.

Was it sticking open or closed?

It was sticking open. When accelerating it felt like the power was down and my wife was telling me that it idled rough but I didn't experience that when I was test driving it.

If you checked it like i told you and found it sticking opening then i would replace the valve and clear the codes and see if any codes come back.

I have the same problem but replaced the valve car still is jerking and misfiring on all cylinders replaced plugs wires cat converter fuel filter air filter fuel pressure is good running out of money and solutions please help