July 12, 2005 Ford Motor Co.'s Explorer and Mercury Mountaineer SUVs are facing a U.S. auto-safety probe because the throttle can stick. The National Highway Traffic Safety Administration in Washington said in a Web site notice Monday that it's investigating unwanted acceleration in 690,000 of the vehicles from the 2002 model year. The agency's preliminary investigation of vehicles with 4-liter, 6-cylinder engines was prompted by 15 complaints and one reported crash. The NHTSA's probe of the Explorer and Mountaineer is a preliminary evaluation, the agency's first step in an investigation. Those probes are closed without further action more than 75% of the time. The rest are upgraded to a second stage called an engineering analysis, of which seven in 10 lead to recalls. Kristen Kinley, a spokeswoman for Ford, said that it was too early in the investigation to determine a cause and that the company was cooperating with the agency