DETROIT — A US government safety agency has opened an investigation into complaints that the throttles can stick on some older-model Ford Taurus and Mercury Sable sedans.

The National Highway Traffic Safety Administration said in documents posted on its website Friday that 50 drivers have complained about the problem in cars from the 2000 through 2003 model years. No crashes have been reported and no one has been hurt, according to the documents.

The probe affects an estimated 310,000 cars that have four-valve, 3-liter V-6 Duratec engines. NHTSA says a cruise-control cable collar can fracture at a mounting bracket and cause the throttles to stick open.

No recall has been issued yet.

Ford s company cannot offer advice to owners of the cars until it determines the cause of the problem, a spokeswoman said.