Q: I have Pontiac G6, it shakes when idle. Usually when I drive and stops on signal. I read some code and it shows P0300 and P0301.

The codes P0300 and P0301 are coming up for a misfire on cylinder number 1. Check the cylinder for spark, fuel, and air. Check the spark plug and make sure that it is firing. The spark plug wire could have a short to the ground if it came in contact with the exhaust manifold.

Also, check the fuel injector to see if its firing by unplugging the injector harness. If the engine stumbles more than normal, then the injector was firing. If there is no change, then either the injector was firing or the cylinder has a internal leak. To check for internal leaks, hook up a compression tester to the cylinder.

Crank the engine over and if the compression is high above 130 psi, then there is no internal leak, however, if the compression is under 130 psi, then there is a leak and could result in carbon build up on the valves or on the piston rings. If the pressure is very low, then there could be a hole in the piston or a bent or burned valve. The random misfire could be a result of the camshaft position sensor not registering with all of the cylinders.

If you need further assistance with your engine misfire condition, then seek out a professional, such as one from Your Mechanic, to help you.