I have a 2013 mk2 Fabia 1.2, a few days ago the accelerator pedal seemed to get harder to press and gave the impression the car is a bit sluggish but I am not sure it is. This seemed to happen overnight.  I replaced the spark plugs yesterday but this made no difference.  The engine runs well, there is to resistance when free wheeling and the gear box feels fine. Any ideas ?

How does the pedal feel if you try to depress it by hand?

I will try it shortly and let you know.

It's seems OK when pressed by hand and does accelerate at the first point of touching it.