Mercury Grand Marquis engine revs unexpectedly when stopping, posing a dangerous situation on Mercury Grand Marquis

Some Mercury Grand Marquis owners report experiencing unexpected engine revving when stopping, which can create a dangerous situation. This issue may arise from a malfunctioning Idle Air Control (IAC) valve, leading to erratic engine behavior. Additionally, some owners have noted that a vacuum leak in the engine system can contribute to this problem, posing a significant safety risk. Furthermore, an obstruction in the throttle body that prevents the throttle plate from closing fully can also cause increased engine RPMs. It is essential for owners to have these issues diagnosed and repaired by a qualified mechanic to ensure safe vehicle operation and prevent further complications.