Check Engine Codes and issues
 

So I will start with some history of the car. 2006 cobalt SS lsj. 2.8 pulley, 60# injectors, injen intake, and zzp 2.5 exhaust. Tuned by RPT. Car was not starting almost every day. I would drive and let it sit while I was at work then it would just click, not even trying to turn over. It was throwing a p0340, p0335, and random misfire code. I had the cam and crank sensor replaced, new balance and timing chain because two guides broke off, cleaned the throttle body, and got a retune. Car ran great then started doing the same thing with a lack of power showing p0340 again. Also was running lean to probably an exxhaust leak. Recently it threw a p1682 and p0340. I know the car needs an IC pump but I don't think that is going to cause the codes or lack of power. I don't know where to even start. I thought about maybe the evap purge valve but that doesn't make sense either. Any help is appreciated...

I had the P0340 code until I finally got a hold of a AC Delco camshaft position sensor. When I had it at my mechanic, they also mentioned to check the harness for resistance and to check the camshaft actuator sensor as well (I didn't need to).

Quick reference: https://www.obd-codes.com/p0340

Sounds like you definitely have electrical problems. P1682 is strange and looks like it could be an ignition switch problem which would also make sense with it not starting. Could also be ECM but I would test the ignition switch resistance first.

The recall for the ignition switch is because the spring that holds the switch in a given state is weak and susceptible to heavy keys turning it off when driving. I doubt you have a switch problem, in 5 years at a gm dealer I have yet to replace one for a no start on these cars. I'm not saying you don't have a switch issue, its just very unlikely. Usually a wiring issue or crank/cam sensor problem for no start/run, if it was one of the sensors it would cause it to turn over but not run so I would lean toward a wiring issue. Always good to check that the ecm/bcm is getting each ignition switch position first. And if you can get to a scan tool it would be good to see if the ecm shows crank request "yes" when it isn't starting.

If you want you can give your vin and ill get you some wiring diagram pdf's.

Attachment 61627
There is a bulletin for multiple codes due to chafing on the engine harness, with yours being intermittent I would lean to checking your harness very good for any spots the conduit is broken or worn. This can cause each one of the codes you have.

And when I try to start it, it'll click and nothing happens. But sometimes it will start and idle and knock then turn off. But if you try again it'll run okay...