One problem related to gas recirculation valve (egr valve) has been reported for the 1996 Mercury Mystique. The most recently reported issues are listed below.
I have had a problem with the engine stalling when outside temps exceeds 85 degrees and the a/c is on. The problem occurs after taveling at highway speeds and the cluch is depressed and the engine is allowed to idle. The engine intermittenly will immediately stall. This causes a partial loss of braking and power steering. This happens about once a day when temps are over 85. The problem has been happening since 1997. The dealer has looked at the car 4 times and has tried fixing the a/c to resolve the problem. They say the I need to bring the car in while it is stalling?.