check engine light

I have a 2000 mercury marquis with just over 200,000 miles.

The check engine light just came on and normally it is steady. However it flashes sometimes. Normally 13 times. We just drove 42 miles at 70- 75 mph and the light stayed on all the time. Coming back we hit some bumps and every time it started blinking. The car runs very good at high speeds and rough at low speed.


Any ideas as to what the problem is? Does the light come on if there is a transmission problem.

I have checked all the fluids and they are ok.

Thanks