GTA IV Cars Textures very low or missing

Hello, I have recently installed GTAIV and I decided to add a few vehicle textures mod. Everything was fine for a couple of days, but today when I opened Gta IV I noticed something really weird: Every texture is completely normal except for vehicle textures. Every vehicle has completely obscured windows, weird square-like wheels, an overall too poligonal shape ecc and the only vehicles with normal textures are the ones that Niko drives. I tried already with some command lines for missing textures bugs and I also rebuilt the vehicles.img file with SparkIV and, since it didn't work, I used the backup of the vehicles.img and the vehicles.ide file, but apparently the problem still remains even without vehicle textures mods. Any help?