P0304, P0342 Code for the 2000 Daewoo Manual Transmission

Hi, My Car runs good. From two months I am get Check Engine Light is On and Off.

I scanned my car computer with OBD II Scanner. And noticed there are two codes P0304(Misfire on Cylinder#4) and P0342(Camshaft Sensor is Low signal). Changed the spark plugs and spark wire but no use. I am still getting Check Engine light on after driving 100 miles. And I am doing re-filling the gasoline then after some time Check Engine is off.

Please suggest the full procedure what are steps I need to take. I already spent $300. The car worth is $1500. Please help me out in this regard.

Thanks
Ram