Could be throttle position sensor (no throttle cables now) linked to ecu... Check with a diagnostic tool, (such as ELM327 or equivalent). Diagnostic socket is under the hand brake lever. With the ignition on and engine off, send code 01 11, wait for response should be 41 01 xx. The xx is a hex number. Should say 00 with pedal fully up. Press down throttle and resend code 01 11. Convert to decimal, multiply by 100 and divide by 255, this gives a position as a percentage. Wait for response if it stays 00. Could be the problem.
Ian Thompson, July 2008