Hello. I didnt know there were forums to talk abot grand marquises, as well as issues with them. This is awesome. Here is my story lol. I have a 2008 Mercury Grandmarquis. I recently have started to notice that when the ac/defrost is on the idle moves up and dow, when it usually stays just below 1000 per minute. I can also feel a slight shake, car does not cut off or anything but it drops to around 400 and jumps back up. Any suggestions would be appreciated! Money is tight so and I have my first son on the way, so i would like to diagnose/repair it myself. My scanner is also not showing any codes being thrown...