I have a 1991 BMW 318is Coupe 118k. When I start the car in the cold, it doesn't idle as though the choke isn't kicking in. When I drive up the road past about 30 houses, the car will idle ok. When the car is then warm, it revs a bit high like the choke is stuck on. I've tried reving it high to turn it off but doesn't work. Since this has started happening, the MPG gauge goes mad. When I stop it goes off the scale. I've changed the idle valve ... any other suggestions??????