While I am new to Toyota diesels, I do have alot of diesel experience. There is no choke on a diesel. The "choke" or throttle blade that these engines have is to allow smooth shutdown when turning the engine off. A hard idle problem once the engine has started and warmed up can indicate a fuel leak (lets air in the system) retarded injection pump timing or a worn out injection pump. Coked up injectors can cause it too, but that can be fixed alot of times by taking the engine for a hard run up the road. Timing belts and chains suffer accelerated wear on diesels because the injection pump puts substantial load on these components. A gear drive setup would be ideal, but most light diesels do not use these setups because of cost. Take a look at your timing belt. A stretched belt will retard timing of the valves as well as the injection pump. The retarded valve timing causes a compression loss at low engine speeds which can further aggravate the idle situation, especially when retarded injection timing is factored in.