I have a 2004 FXT @ 100K. Engine started to idle at very low rpm, around 5oo and less, to the point of almost stalling. Just had new plugs put in a week ago. I have cleaned the MFA sensor as well as have done the Seafoam treatment. Car runs fine with acceleration above 2000RPM. I also had valve gaskets replaced last week so I am assuming there is no valve damage/problems otherwise that would/could have been detected?...Maybe I need to check coil? Fuel Filter? Fuel pump? I will be picking up a diagnostic reader to get a code tomorrow but looking for other ideas. I know I have a bad rear 02 sensor but maybe front is going? Help!