My car has a gremlin?

When I operate clutch engine revs to 2 or 3 k rpm! Sometimes! When this happens temperature gauge drops to 0 as if electrics are off! any ideas ? R try avensis.... was thinkin maybe fault on ect sensor but don't know where it is on this car.... engine management light comes on when. It happens but goes off after also..... help me I don't wanna scrap my baby and don't have money for garage fix!