I have a ford focus zetec s 2010 1.8 petrol engine,

I'm having a real issue when driving at a constant speed on motorways travelling at 60mph 70mph etc.....

The car feels as though it is being dragged back then released. I have changed the air filter and sparks and also tried fuel cleaner. But no join as of yet.

Many people I have spoken to say its sounds like fuel starvation, but the car has a built in fuel filter, so not sure when to go with it next ? It's only done 32k miles could if be a sensor or MAF on such a new car?? .

Thanks for your help