A few weeks ago i was on a nice clear stretch of road so but my foot down. When i got so the end of the road and slowed down the revs were all over the place and and i had to keep revving it up because it looked like the car was going to cut out. Today i was on another clear road so though i would test it out again and put my foot down, sure enough as i come to a stop the engine felt like it was going to cut out. After driving the car for a few miles it seems to sort itself out. Any ideas what's going on ?