Intermittent Loss of Power - Heat Related?
Problem started a few weeks ago, occasional loss of power which felt as if the brakes were gently applied for a few seconds. Car was booked in for a check but the day before whilst on the motorway (15 miles) the car was fine until I went to move into the middle lane to overtake a lorry. Pressed the accelerator and nothing happened, dropped from 6th to 5th, nothing happened. Aside from losing speed there was a huge amount of black smoke.
Car went into the garage and they changed the EGR valve, no errors recorded, fuel filter replaced as well. Picked the car up and it felt fine on the short (5 mile) motorway trip home. Following day on the motorway (20 miles) exactly the same thing happened. This time the MCSF light came on and almost no power to move the car. Car returned to main dealer. EGR valve identified as broken and replaced under the warranty.
Again, picked the car up and it felt fine until 15 miles on the motorway and complete loss of power again. Car returned to garage and I got a hire car. Garage checked the car, no errors recorded and they could not replicate the problems at all.
What on earth could cause nearly all the power to vanish coupled with black smoke after 15 -20 miles on the motorway and then fix itself for short journeys?