A 1990 BMW 735i from the UK may not meet U.S. emissions specifications, but might be possible to import as a gray-market vehicle. This process can be expensive and time consuming.
You should review what the Department of Homeland Security, Customs and Border Protection (CBP) has to say on this subject, as CBP controls what vehicles may be brought into the United States.
Your intended vehicle must clear customs before it can be registered in any state. The costs to modify and certify the emissions and safety equipment on a gray-market vehicle are considerable.
We recommend contacting the California Air Resources Board for more information regarding the import, emission test, and registration for this particular 735i BMW. The ARB number to call is (800) 242-4450.