Throttle cut during cruise (Diesel)

While accelerating or maintaining a constant speed during normal driving, the gas pedal suddenly becomes unresponsive as if I took my foot off the gas pedal. It fixes itself when I take my foot off the gas pedal and press it, but it lasts for 2-3 seconds. This doesn't happen all the time. Does anyone know a solution? Diesel 206 2003

The problem was solved with the brake switch. But now it stops and does not start (it starts only after 2 minutes of rest). The fault light comes on and then goes off.