Hi im ctg i need help
There have 3 problem in my car system
is there have a way to make cylindrical-constraints just stay in 1 spot and it only can rotate to left and right?
every help will very appreciate
first of all nice i take it you are using ikcontrols for the arms on the steering 
very nice not many people taking advantage of that will have to show you some stuff i have been working on with that too
a few things you can do to help the vehicle with the problems you are having.
for the cylindrical constraint that im guessing is the back wheels, you can definitely change the limits on the cylindrical constraint to make it more like a hinge if that’s what you are asking about for that one (or you can just use a hinge of course.)
set the LimitsEnabled to true and then reduce the Upper/LowerLimit to be the same or very close if you want it to have a little “play” in it. probably want to keep restitution at 0 though or it will likely bounce about more violently and i would have thought you want actuator type on the slider to be None unless you are going to like push it out one way or another.
make sure to use cylinder parts as the wheels not meshes. Make the meshes just a visual part welded to the roblox part that is the “real” wheel as it will calucluate the cylinder rolling as if it is actually cylidrical whereas the mesh it will treat as a many sided shape giving a far more jittery unpredictable ride.
make all the parts on your vehicle massless and have just one part (you can have more for more advanced vehicles of course but keep the number low) that you use to put the mass of the vehicle where you want it. for a go-cart like this you want it REALLY low in fact you might even want it under the ground! the mass part can of course be cancollide false it is just picking how the vehicle behaves 
that will also make it self righting when you do flip it.