Rodeo engine revs



We have a 2001 Isuzu Rodeo with 63 thousand miles with a problem that has been present since it was bought. The dealerships have not been able to identify the cause. At times, sometimes when it is could and some times after it has been driven for 200 miles, the engine starts to race like the cold engine on a car of several years ago. This may happen once at a stop sign or on start up or it may happen several times during a trip. It also may happen for a period of time off and on and then not occur for a week to a month.