Originally Posted by josiahg52

Assuming you have a diesel, the TB stays open a majority of the time. It only shuts briefly during engine shutdown to eliminate shudder and then reopens, will shut in a runaway diesel engine scenario in an attempt to shut the engine down, and will vary in position during DPF regeneration in order to trim the air entering the engine when the regeneration process is adding extra fuel post compression-ignition in order to maintain RPM and power output at the level the operator commands.

Again assuming you have a diesel, EGR valve position varies during engine operation.