car coasts ?

hello, my Dad has a 2008 Focus w/auto and i drove it today because he's been complaining about the car coasting through the city at 30mph with his foot off the gas pedal. He also complained about it taking a long time to reduce the speed when he takes his foot off the pedal. He took it in to the dealer and they couln't find anything wrong with it. Now when i got it up to 40 mph and took foot off the gas it took .3/mile to drop down to 20mph. On the flat it also seemed to me that it wouldn't drop below 1000rpm and 20 mph. i did at one time see the tach actually jump up to 1500rpm with my foot off the gas pedal. Why would the rpm's increase going down a hill with no foot on pedal, mph i would expect. thanks for any comments or input you have on this subject..Randy

The butterfly flap on the throttle body may not be closing all the way. With the engine off open and close it several times. Is it coming back all the way? Try some throttle body cleaner. The vane may not be closing all the way. Does the return spring on the throttle body have enough tension to pull it shut? I don't believe there is anything wrong with the cruise, if it has it.