Hello, no recalls I am aware of. Contact your local BMW dealership with your vehicle identification number (VIN) to check for any open recalls on your vehicle.
As far are your steering concern, Testing would be best performed on your power steering system, inspecting fluid, sensors, steering gear, pump and other mechanisms to see what is going on.
RepairPal Certified shops can diagnose and repair your 2004 BMW Z4. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.