my VW golf match year 03 has been in and out the garage over the last 3 weeks. The problem is intermittent: upon starting the engine the car revs by itself, I can hear and feel it revving and the Rev counter is going up and down. When I drive off it lurches along very slowly, has no real power and won't get up speed. The garage has changed the throttle housing. it was fine for 3 days then the problem recurred. The mechanic has not experienced the fault directly as it has always started fine when he's had it. Any ideas?