Maybe the throttle is sticking?

The throttle pedal is connected by a cable to the engine. Your problem
sounds like the cable is sticking.

You can test this by raising the hood (bonnet) and starting the engine.
Then, operate the throttle plate by hand. This test will allow you to bypass
the cable that is connected to the gas pedal. If the engine responds
properly, the speed drops reasonably quickly to proper idle speed, then it
confirms that the cable is dirty.

The throttle cable is constructed like the brake cable on a bicycle, there
is an outer casing that remains stationary and an inner cable that is
connected to the pedal at one end and the throttle plate at the other.
Normally, you can use a spray-cleaner that you squirt into the throttle
plate end of the cable, and work the cable full travel several times until
it operates freely. It is possible that the cable housing is actually broken
at one end or the other, so a close inspection would be an important part of
your repair effort. The cable housing must be secured at each end. If it is
not secure, it can move - and this can cause the cable to stick when you
take your foot off the gas pedal.

Good luck, I hope my english is understandable since it is obviously not
your first language.

Is the mat in the footwell interfering with the throttle pedal?

Andrew