Renault Kangoo kangoo 1.2 completely loses power

It starts , but sounds rough , it's inclined to stall while idling, the problem is that it suddenly loses power completely( foot to the floor , nothing happening .) after driving a short distance.( it varies but never goes further than a mile from a cold start ) However we have found that if we start it , rev it for a few minutes, then switch off for 3-4 minutes it’s fine drives long distances with no problem at all and an bestopped and started again no problem. We have renewed the distributor, it’s had new spark plugs, new accelerator pedal and potentiometer, Auto electrician did a diagnostic test , replaced the sensor to the throttle body , any ideas please? The mechanic says it’s electrical , the Auto electrician says it’s mechanical ?