Q: Car has been misfiring 2007 Mercury Mountaineer

Hello - first task is to check for problem codes, whether the Check Engine is lit or not. If it is, there should be an indication of which cylinder is misfiring. Misfiring can be ignition related - plugs, coils, timing sensors, or fuel related - leaking or clogged injectors, or caused by air leaks. If no code, the problem may be random, and caused by air leaks in the intake manifold (your mechanic’s comments suggest that). I would recommend an engine misfiring inspection by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.