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
Look for a vacuum leak, if your transmission has a vacuum modulator look there. You can also have the EGR valve tested, they can stick open or closed at the wrong time.
If it is indeed one of the above, what would you estimate the cost would be. Question two, would you concur it's not the belts and or motor mounts. Thanks, Paul
Try some Techron in the gas tank before spending a bunch of money on repairs.