if the ecu detects any voltage abnormalities in the accel circuit it will put the engine into 'slow mode', this will also happen if there is a problem with the throttle body sensor voltages.

there is probably nothing wrong with the ecu itself.

try replacing the accelerator pot first
if that does not change it then the throttle body is next
if the internal mechanism in the throttle body gets dirty and keeps the sensors from making thier full sweep, or in some cases i have seen the wiring connections to the board inside them break, this can cause it to error out and put the engine into 'slow mode'. And as far as i know on those particular TB's they are not accessible, they are riveted shut and are not meant to be accessed and repaired or cleaned.