rafterq

Yep, re-installed a clean copy of the mods folder, all working now with mods istalled, Thankyou @Kal74, the only other thing in that mods folder that i changed and did'nt replace was the carvariations file, so must of been that or something, Issue resolved. 

Happy to hear it worked for you. Sorry to hear that the issue turned out to be in your mods folder.  It happens more often than not to people.
 
If you can figure out which car mod is causing the problem, you can try to fix the issue or remove it. You should be able to use police vehicles and LSPDFR Plugins without issues. If you can't figure out which mod is causing the issue, then all you're left with is to start over modding your custom vehicles. My advice is to do 1 car mod at a time, each time launching the game and testing to be sure you don't run into any crashes or other issues. If I was a pro at that car modding stuff, I would try to help you out, but I'm not.
 
Personally I use Modding DLC Pack V by Albo1125. His guides and video tutorials make adding/replacing vehicles, peds and weapons an absolute breeze 

If you bring up your phone in game, there is a save option in there. You can also save by sleeping in a bed. There might be a shortcut key, I think its F5. Yes get to Free mode where you can roam around and save then. Then exit the game and launch from RPH

I'm very thankful for yer help, friend! Have a fine evening!