One problem related to engine has been reported for the 2008 Mercury Grand Marquis. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2008 Mercury Grand Marquis based on all problems reported for the 2008 Grand Marquis.
On October 27, 2010, my wife was driving with me in the car and she started to brake for a red light. She was going about 30 miles per hour. As soon as she applied the brake, the engine accelerated and she had to use a large amount of braking pressure to stop the car. As soon as the car stopped, she took her foot off the brake and the engine returned to idle. Yesterday, I was driving the car at approximately 55 mile per hour and started to move into the passing lane when the traffic light ahead turned red. I applied the brake and the same thing happened. I had to apply a large amount of pressure on the brake peddle in order to stop the car while the engine raced on. As soon as the car stopped, the engine returned to idle and the problem was over. Yesterday, I took the car to the dealership where it was purchased and they kept the car overnight to run various tests. They found nothing. I picked the car up this afternoon and am going to now take it to another dealer for inspection.