Engine code of p505 idle control system malfuction what does this mean and how do you fix it?

More than likely it's your IAC or Idle Air Control motor. It's usually right on your intake cover somewhere, check with your repair manual to find out what it looks like and how to remove it. If this isn't the problem check with your EGR valve, however usually the EGR is a nother code in itself. Good luck and make sure you perform the proper Drive Cycle for your car before getting it inspected, or take it to Advance Auto to delete the code.