Ford Fiesta engine dies at higher revs, any ideas?

Sounds like your air filter needs to be replaced. hopefully thats all it is.

Are you in motion when it stalls? or sitting still?
There are 3 components to look at. Fuel, Air supply and spark.
Worn throttle cable can limit fuel also.
Fuel filter , air filter , fuel pump etc. The engine runs so you can eliminate spark.
With a little more detailed information you can narrow it down.

Mitchboogie
July 2005