2005 Vue, 2.2L Ecotec, around 200k miles. You will be driving, and the car will start misfiring. Very low power, frankly feels like it's running on 2 cylinders. The ONLY code it sets is P0300. It might do it for 30 seconds, or a couple minutes. Then it runs great again. I have replaced both O2 sensors (it previously had an engine too rich code which is resolved), and the ignition coil pack and module. All data while it's misfiring looks normal. I've never had anything like this that did not set codes. I can drive it for days and it's fine, runs great. One thing that I have noticed is that the cooling fan runs constantly while it's misfiring. Once it stops, the cooling fans shut off. The ECT via the gauge and also the scanner read accurately.
