Go with what Mike says. I would guess your machine has glow plugs similar to my LX665, that is they are the 15 second ones not the earlier ones you used a longer glow on. Last winter mine became hard to start, checked the plugs with a ohm meter while they were in but disconnected. 3 were the same and the 4th was somewhat different. Took them out and the one did not glow. It made a huge difference in starting to replace that one.
However you say yours will only start on full throttle and if it sits for a bit it is hard starting. I would think that is more a fuel or engine condition problem. Even when it it 0 degrees out if I run mine and leave it sit for a couple hours it will start with little or no glow. I never have to use more than high idle throttle when starting it. But it also has synthetic oil in it so it spins faster and the turbo gets oil right away.