Its not your fault, its PD's. Nothing you do to your connection is going to stop you from getting kicked from certain lobbies. I have had luck, however, looking for the following criteria
1. FIXED HOST. I don't know why so many people don't check this box, but when it is checked I never seem to get kicked
2. Less than 16 max players, and if there are 16 make sure there aren't a lot of people perpetually "loading" even though they are on the track (you can't see them, and I don't think they are counted towards the total player count, so when someone else tries to join somebody gets kicked, thats my theory)
3. *** race quality 5 bars of reception. **** can be iffy, a lot of people push their hosting capabilities farther than should be allowed. Unfortunately you cannot tell what the voice quality is set at, because with 16 players at the high setting, its bound to crap out. Thats just wayyyy too much of a bandwidth hog