Sounds to me like it could be a clutch shoe spring that has snapped, causing the clutch to bind. If this has happened the engine will be engaged at no matter what rpm the engine is doing and will not idle. Pull the clutch bell off and take a look at the clutch shoe springs and see if any are broken. this would allow you to start the engine at higher rpms and driver it aslong as it doesnt drop back to idle.

bigstu