Hello all had a code for p0455 which was a large leak in the evap system I replaced the vapor canister purge valve let the car run for a bit I read the code again and now it's p0300 random multiple misfire and the evap code was not there I do have a REALLY bad exhaust leak where pipe meets the muffler is absolutely disconnected rusted after years and eventually cracked and broke I am waiting on a new full exhaust until then I was wondering if the broken exhaust would cause the misfire I just feel it's fuel related because of the purge valve I replaced and the misfire code was not there prior
Any insight would be helpful

 

A leaky exhaust can cause the engine to run inefficiently. These sensors and the ECU are so sensitive these days, that if the O2 sensors are operating at 95% efficiency, a code can be triggered. I'd suggest fixing the leak, as you seem to be doing, and then clear the codes and see if any pop up.