That sounds to me as though it starts OK/better when warm/hot and also has idling issues.
I jest about my L Series Freelander, but the reason you can't find much help is probably because the L Series is a bloody good engine.
If its got idling issues then its not glowplugs, they're only on at start up. So you're looking at fuel/air flow. Changing the air filter was a good start, it does make a big difference, mine stopped smoking after changing the air filter - although I've never had problems starting. So I've never had to diagnose starting issues.
You mention smoke, does it smoke much when driving? If it was a fuel timing issue, I'd have though you would be getting smoke all the time. On the 2 1/4 Series engine white smoke is a sign of poor timing on the fuel pump.
