i have a duel fuel el 4.0i6, when i accelerate over 1000rpm it will hold the revs and happily cruise down the road like its on cruise control,usually between 1200-1700 40-60km/h+, fuel consumptions out the window and 40kmh school zones need to ride the brakes or use cruise cont. just to keep th right speed, could this be the idle speed controller ive heard about?, only seems to happen in gear too, out of gear it only holds for 2-3 sec then returns to 7-750rpm, around town when coming to a corner/turn car will stay idling 1100-1200rpm, any help with this problem much appreciated, thankyou-stonghold05

check for vacuum leaks,or sticking throttle cable/sticking throttle plate.