I have a 1989 Porsche 944 non Turbo. Im the only owner, car has been maintained and has 39,000 miles The car when I start vibrates and is noisier than usual. When I've driven the car , the car runs smooth and normal when driving. The problem is when your stopped at a light or in traffic. The cars sometimes will start to idle ruff like it wants to stall out. Hasn't stalled out yet, probably because when this happens I shift it to neutral and give it a little gas. This issue began when I put the car back on the road after sitting for 7 months. I did use fuel stablizer for storage. I have used up the tank of gas in the car and refilled with 93 octane to no avail. I have had the timing belt changed. Any comments would help. Paul