What happens to temperature in the throttling process? Does internal energy change in throttling?

For throttling processes,

internal energy + flow work = constant

If we talk in terms of internal energy and flow work, If flow energy increases during the process it causes the internal energy to decrease. Temperature is directly dependent on internal energy hence in this case the temperature reduces. On the other hand, if the flow energy reduces downstream (the work required to push fluid is less at the outlet) and internal energy rises the temperature of the fluid increases.

The magnitude of rise or drop in temperature is decided by the Joule-Thomson coefficient.