I have a Fiat Brava SX80 1.2 16V which suffers a severe power loss on motorways when reaching 60mph. The power drops off and the car coasts to a stop with the engine at idle there is no response from the pedal. When you turn the ignition off and on again you can proceed as normal for a few hundred yards then the problem comes back. When driving in town traffic the car is normally ok for a few miles then the same thing happens. The car recently had a replacement engine fitted (second hand before I bought the car) the mechanic at the garage said everything was done that needed to be done so should be ok. I have changed the plugs and leads and also put an injector cleaning additive in the fuel, but the problem has not gone away. No warning lights come on to warn of anything wrong. Any advice.