[lavamike]

Invisible cars happen when they are in a different interior than you are.

Put players in a different interior: SetPlayerInterior(playerid, interiorid);
Put vehicles in a different interior: LinkVehicleToInterior(vehicleid, interiorid);

https://sampwiki.blast.hk/wiki/SetPlayerInterior
https://sampwiki.blast.hk/wiki/LinkVehicleToInterior


Hope that helps!
-Mike