Idle issues
 

I have a 2003 Mazda B3000 with the 3 liter engine. I have already replaced the idle control valve and the throttle control sensor. The problem I have is that lets say I am driving at 35 mph and take my foot off the gas, the engine will continue to run at about 1200-1300 rpm. If I apply the brakes and come to a stop the idle will drop to the usual sub-900rpm range. This is not a really big deal but the truck will continue to run at more than 20 mph. I would like to correct this myself if possible. any help would be appreciated.