My sputtering, backfiring, and stalling returned Sunday night. Same P0300, P0301, P0303, P0305 codes. They tested and replaced the fuel filter and it ran better but then she threw a code for the MAFS. I would have cleaned it but Cadillac won't clean, only replace. That pissed me off but I figured better to start with a fresh new sensor than one with 121,000 and residual dirt after attempting to spray it clean. Anyone with those symptoms try disconnecting the MAFS. It should run much better without it plugged in. It'll fail emissions testing and probably waste fuel but it'll get you home. Nothing will help a clogged fuel filter except replacement and after 121,000 miles a new one is due. I've said it before but this time I didn't follow my own advise. Most of the troubles with this car are due to sloppy maintenance. Mea culpa, mea culpa, mea maxima culpa.