The National Highway Traffic Safety Administration says it has 50 complaints about sticky throttles in the cars from the 2000 through 2003 model years.
The probe affects an estimated 310,000 cars that have four-valve, three-liter V-6 Duratec engines.
No crashes or injuries have been reported. 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.
The Ford Taurus and Mercury Sable and are nearly identical cars. Ford ended the Mercury brand two years ago.
(Copyright 2012 by The Associated Press. All Rights Reserved.)