Over the past couple of months my car has started shaking when I'm stopped at a red light or stop sign. The RPM gauge will fluctuate up and down when it does this. Then to top it all off the "Service Engine Soon" light came on the other day. The car has 79,000 miles on it and runs well other than this problem. I'm taking it to the mechanic this Friday, but I was just wondering if anyone has any idea what I can expect??