cold water pressure low in new faucet
 

Plumber installed new faucet, the cold water worked fine for 4 days then pressure dropped to less than 50% Kholer sent new valve, no difference. They had us switch the cold line to the hot to see if it would work--it did. Tried hot water tubing on cold but same result low pressure. Kholer says not their problem. Ideas?

Sounds like loose floating debris in the cold side of the faucet.
Turn the water off, dismantle the faucet and cover it with a towel.
Turn the water back on very briefly to flush the debris out of the faucet body. That should clear it. Been there. Done that.
Sometimes, you have to take a small Phillips head screwdriver or an icepick to break up the little hungup piece of debris so that it will flush out.
Good Luck!
Mike