1999 Volvo C70 engine not running correctely

Engine Mechanical problem
1999 Volvo C70 4 cyl Two Wheel Drive Automatic

the rev counter goes up and down when driving and stationary also when driving it loses power I then have to take foot off accelorator push pedel back down to resume normal power I had the air in flow and spark plug coils tested and spark plugs changed the rev counter still goes up and down. It's also a bit hard to start as well they plugged it into computer it says it was other problems. But it's not what comes up on computer