Hyundai Excel 1994 engine surge problem

I have an Excel (I think they are sold in the US under the name Pony) and
it has this strange problem were at random times the car engine speeds up to
maximum. If I wait about 30 seconds the engine goes back to idle.

I tired to reproduce the problem by running the car on idle for half an hour
but it runs OK.

I have tuned the car replacing spark plugs...

The service manual says it can be a vacuum leak or fuel problem.

Has anyone had a similar problem?
Would you have any idea where the problem lies?

I was going to try replacing the fuel pump and fuel filter first.
Does this sound like I'm on the correct path?

Thanks for any assistance.

 

I have a 1995 Hyundai Excel Sprint. After just having a major service and
tune, I am experiencing the almot the same problem.

What started as just a "lacking fuel" feeling problem, it has now
increased to occurances of driving along at 100Km/H and a chugging (pull
back/hesitate) problem oocurs. This happens also when driving at any speed
and circumstance. Obviously being very dangerous, I have decided not to
drive until I can find an answer.