[RNRea]

The engine running rough enough to cause the shakes isn't too good. The fact that the service light came on says that it is likely a problem with the ignition system (fuel injection systems could also possibly do the same, but it is less likely). If it hasn't been serviced in a while, you might be up for a new distributor cap. The ignition module could be going bad, but I suspect that they typically just die (like mine did) and the engine won't start at all. A bad coil will cause weak spark and could be an issue. I would replace the cap and rotor along with the coil. If the plug wires are questionable then they should be replaced too. I would venture to say that the plugs should be replaced, especially if they are the originals. Get the best quality parts, don't go cheap here (I prefer Napa Auto Parts for ignition and electrical in general), but I wouldn't rule out Delco parts from the dealership either.