2000 Chrysler Concorde Troubles starting and stalls idling

Hello,
I have a 2000 Chrysler Concorde lx 2.7 L EER V6

I have been having issues staring it, after a few cranks it starts and while idling at stop signs it some times stalls are comes very close to it.

I got codes
1684 saying the battery has been disconnected within the last 50 starts
and
0340 camshaft position sensor

i replaced the camshaft sensor and am still having the same issue. The 0340 code still comes up.
I had it checked by a Diagnostic machine and it said that the camshaft sensor wasnt reading and the crankshaft sensor.

Could it be a bad camshaft sensor? The wiring from the camshaft sensor to the computer looked good. Or should I replace the crankshaft sensor?

Where is the crankshaft sensor and its it something I can replace myself? If not about how much would it cost if I brought it to the shop?

thanks