I own a 1987 Mercury Grand Marquis (302 V8). It has about 126,000 miles on it, but still runs great and very reliable. However, I have noticed over time that the car has become increasingly shaky and rough, both while driving and in neutral or park. This roughness is not bad at all, but it is noticeable. Is there something that I can work out so the engine will run a little smoother? Or is this what happens to engines with over 100K on them?

I believe the spark plugs are due to be changed, but the car doesn't skip or anything when accelerating. Would changing the spark plugs help the smoothness of the engine?

Any help would be greatly appreciated!

Changing the plugs might make a difference. When engines get to be high-mileage, sometimes the cams wear down. The valves aren't opening as much as the used to, and sometimes cylinders don't all get the same amount of air and gas due to one or more lobes on the cam becoming worn. Not a huge concern, just keep up on your maintenence.

thats what has happened to my volvo. the cams have worn down and its running rough. althought it has started to stall when I put it in drive or reverse. I believe that it might have somthing to do with the AMCU.