power steering on 2006 Chevrolet Malibu

power steering goes in and out. When it is out it is worse than driving a truck with no power steering. It does not have a power steering pump, took it to a chevy dealer and they couldnt find a problem.

2 answers
This is obviously very dangerous. The electronic steering is having an issue, I'm surprised the dealer hasn't been able to address it.
I would take it back to them and make sure they have checked all the technical service bulletins (TSB's) from GM, checked for recalls and checked for and diagnostic trouble codes in the vehicle computers.
Sounds like you have electric power steering and maybe try an independent shop here and explain on the phone what the problem is http://repairpal.com/directory?address=46802&car_brand_names=Chevrolet