I'm a newbie and woman that knows nothing about engines and need some advice. I took my BMW 320i (E90) in because the engine lost power and the car “shakes” on idle as if it's going to stall. The shop advised it's the coils that need to be replaced, so I paid for that to be done. Took the car and drove 50km and engine light comes on (yellow)... drove it back to the shop and now they say it's the valve stem seals and valve stem sensor that needs to be replaced. The car was making light smoke on idle and using more oil than I think is normal before but I didn't take it in for that. Am I on the right path, is it the valve stem seals that need to be replaced and also the shops says its about R8000 for the seals and another R8000 for the sensor?