P0300, P0302, P0304, P0306, Engine running rough with little power

[Perrier]

To original poster

I have experienced similar codes and after a lot of money spent on replacing possibly failing parts I found the following, and corrected both the misfires on multiple cyl and the Evap error code:

Opened the spark plug cover and found water and oil around the spark plugs. This was due to failure of two gaskets, the valve cover gasket caused oil leak, and the spark plug cover gasket allowed water splashes to get through to the plugs. I replaced the gaskets, cleaned the plugs and connectors. Started the car and it ran smooth and the codes reset themselves.

For the Evap code, I put some silicone spray on the gas tank cap and closed it tightly. Reset the code, and it hasn't come back (approx 5months ago)

Try these things before spending a whole lot of money.