How do you byipass idelshutdown on Volvo semi?

It's programmed into the ECM. There's a number of ways people attempt to do this, but how successful they are depends on the ECM programming. You can try putting the vehicle into high idle... sometimes that works... you put the cruise control on while the vehicle is parked and the brakes are engaged, then use the "Resume/Accel" button to increase the idle. However, a company might disable this feature, or set up the ECM so that the idle shutdown timer remains in effect while in high idle.

You can try keeping your trailer brakes locked and your tractor brakes released.. it may or may not work, again dependent on what's programmed into the ECM.