One problem related to vehicle shudder has been reported for the 1999 Mercury Grand Marquis. The most recently reported issues are listed below.
Vehicle would shake violently at any speed from 45-80mph. Took to a mechanic said the front end needed to be replaced. $800. 00 later it still did it, then took back said the tires needed to be replaced although we had 80,000 mile tires, and only had 35,000 miles put on them. Replaced the tires for $600. 00. Still shook, took to a different mechanic said it was the transmission failing. During scheduled maintenance found cracked intake manifold, antifreeze and oil in spark plugs, cleaned out changed spark plugs, ran fine until the manifold leaked more coolant into the spark plugs and now we are at square one. Researched online found a bunch of places saying it was recalled, when I called the dealership they said no recalls. Price of replacing the part was $615. 00 if I had one alternator, or $650. 00 if I had another.