Starting and power problem, code P0240

The other day when I started my car there was a dramatic loss of power. No matter what I did I could not get the RPM's over 3,000 and the car above 10 MPH. I turned it off and it barely started again. I was able to limp about 5 miles home. When I got home, I tried to start the car and it would turn over, but would not catch. The next day I started the car with no problem and it drove with no problem. When I stopped to get gas it would not turn back on. It did start with a jump though. Now whenever I turn the car off, it will not start unless I jump it. If I let the car sit for approximately 30 minutes though it starts right back up. The only code is p0240. This code has been on for about a month. I have absolutely no idea what could be causing this problem. The low power issue when driving has not recurred.