I have a 2001 Chevy 2500 HD 6.0 and all of a sudden it started idling rough and threw codes for random multiple misfire and throttle position sensor. My mechanic replaced the throttle position sensor and told me that the misfire was due to bad feul injectors. I've ran cleaner through the fuel tank for 5 tanks of gas with no results. Since the problem started suddenly and it only happens at idle after being shut off for a while, I'm not sure I'm buying the problem being the injectors. Also, about the same time this all began, my battery has began dying if I leave anything plugged in overnight- like cell phone chargers or Bully Dog tuner. Could the misfire be related to the battery? Or are the injectors the more likely culprit?

 

Not up on the newer engines but whats the fuel pressure when it is doing this?maybe some leaking intake manifold gaskets?to test for the extra draw on the battery you can disconnect the positive battery cable and hook a test light or multimeter set to amps between the battery and cable and see how much it is pulling then you can go start pulling fuses to see what makes a difference maybe that will point you in the right direction

 

I would like to suggest you to perform a fuel injector balance test for all 8 cylinders, then inspect O2 sensor connections on the misfiring bank for corrosion or water intrusion. If water intrusion is found, it may be due to the AC evaporator condensation dripping onto the O2 sensor harness. So try to repair the connection. Finally, check for excessive exhaust back-pressure using the exhaust diagnosis.