82 300sd white smoke rough idle

It sounds like a bad headgasket. White smoke indicates coolant is getting into the combustion chamber. When it burns, the smoke is white. I would recommend having the engine compression tested and a cooling system pressure test to see if it pressure drops. Check the motor oil to make sure there is no coolant getting into it.

I don't have away to check colant system but compression is from front of engine to back of engine by firewall 1-310 2-300 3-0 4-300 5-315 don't know what to do know or were to start

Cylinder 3 has 0psi? If that is the case, I have a major concern. Even a bad head gasket will allow the cylinder to build compression, just lower than normal. That sounds like a stuck or bent valve or a hole in the top of a piston. Does the engine have a dead miss? Also, (after thought), you mentioned you had the valves adjusted. I question if the mechanic overtightened one allowing one of the valves on cylinder 3 to stay open.

No matter what, cylinder 3 is where the problem is. Exactly what is causing it is the question. To determine that, I would recommend the valve adjustment be rechecked on that cylinder to make sure the valves are seating shut and not over tightened allowing one to stay open. If that isn't the case, then the head needs to come off to check if a valve is bent (sticking open) or there is damage to the piston. Again, even a bad head gasket will allow compression to build to some extent. With 0 compression, something is wide open. The odd thing is all other cylinders are excellent.

Have that checked and let me know what you find. Just for the heck of it, try this little trick at home. With the engine cold, remove the radiator cap and start the engine. Let me know if coolant sprays out when it starts.