Grand Theft Auto 4 (GTA 4) Message Board  

If you downgrade the game, the trainer works. Here is the link for the downgrading, also mods, and multiplayer work when you do this. I have personally tested it and it does work. However it does bug the game a lot, for some weird reason. People have created a new trainer that works with the new patch, however its extremely buggy.

When downgrading the game, use this link to download on the steam site it doesn't work.
1.0.7.0 link:

parche-gta-iv.en.uptodown.com/windows/download

How to guide
Link:
steamcommunity.com/sharedfiles/filedetails/?id=810729251

My YouTube video with the trainer working:
www.youtube.com/watch?v=CrcSDpkzJzA&t=220s

Enjoy and have fun!