po 300 and idler off wranger

Check ingnition coil and plugs, also check vacume leaks and a smoke test around intake.If these check out good, than check for a burnt valve. Do a cylinder pressure test, Go to Youtube and Scotty Kilmer has a good vidio on how to do this,You might have a bad piston ring on a few cylinders, To check valve you will have to remove the head.Also you can do these in any order.But the spark plugs and coil check at the same time just to eliminate the spark problem.Than vacume and cylinder pressure test