I'm trying to get 100% on GTA IV to get the Keys To The City achievement but I'm stuck at 95%.

http://wikicheats.gametrailers.com/Grand_Theft_Auto_IV_-_PS3_XB360/Achievements

I saw that some people are stuck at 99.5% and they said this half percentage point is a random encounter.

What do you think is missing on my game? I already had done everything on the checklist...