DETROIT (AP) — A U.S. 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 in the U.S. that have four-valve, 3-liter V-6 Duratec engines. NHTSA says a speed-control cable collar can fracture at a mounting bracket and cause the throttles to stick open.

No recall has been issued yet. Investigators will determine whether the problem is bad enough to cause a recall.

Ford says it is cooperating with the agency and doing its own analysis. The company can't offer advice to owners of the cars until it determines the exact cause of the problem, spokeswoman Marcey Zwiebel said.

"Until we are able to gather more information and complete our own investigation, we cannot speculate as to what actually occurred during the reported incidents," she said.

The Ford Taurus and Mercury Sable and are nearly identical cars. Ford ended the Mercury brand two years ago.