1997 Honda Civic IDLE

Car runs fine when you are on highway but when it stops or is in netural the engine keep accelerating itself up and down. My mechanic adviced that I drive the car for about a week or so as car is trying to find its idle. He believes that since I brough this car recently the last owner must have not driven it for a while and that why computer lost its memory for idle and now its trying to find it.

Please advise if I should be concern aboud anything else or ask my Mechanic to check something else to fix this issue