This happens to me too sometimes. Although, I do not have car mods, or anything other than LCPDFR 0.95 version. And it works perfectly fine then it freezes and says "GTA IV has stopped working, Windows is looking for a solution to resolve this" So I just put in another version of GTA 4. I used to have 1.0.4.0 but I downloaded 1.0.7.0, it works then it freezes. Maybe if I download another version and install it, then finally, I could play GTA IV.