Well, I got my 996 out last night after dinner while my wife and daughter went to go Pokémon-ing. It fired right up; and I pulled away. 1 minute into the drive the idle goes super erratic and then boom ABS/PSM lights; which are a signal for MAF being disabled and going to stock fuel maps.

I putter around for a minute or two and then pull over and start it back up. I’m thinking it’s just a fluke from sitting for 2-3 months.

It actually seems a little better; idle is a little wonky but better. No ABS/PSM lights.

Get to the gas station; fill up. Go to leave and my car dies. I’ve had some strange warm start issues, which I’ll get to in a minute; but never had it stall/die like this. Took three times to get it fired back up but eventually it did. ABS/PSM light came on. Got 2 blocks from home and the car stalled at idle again as I was coming up to a stop sign.

It wouldn’t stay running. Started and then heard a ping and it died.

Unplugged the MAF. Started fine and drove into the alley and garage seemingly normally but I was so close who knows.

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So signs point to a possible MAF problem, or a fuel delivery problem, or a vacuum leak; since it sounded a lean condition leading to a knock when it died near my house. And at least based on yesterday vacuum seems less likely because it started fine cold.

I recently installed some new upstream o2 sensors and I’m not sure if they are causing the car to run lean since I didn’t unplug the battery or reset the ECU. I’m thinking if long term fuel trim had adjusted because of fouled sensors and then the new sensors went in then it might cause it to lean out suddenly butttt; I don’t know. I reset the ecu after the drive and will try another drive(although I’m also going to check for vacuum leaks and maybe fuel pressure). If still no luck I’ll have to also check voltage from the o2 sensors and maybe put the old ones in. After that I suppose clean the maf and it’s connections. Check intake air temp and coolant temp sensors on my obd2 app. 

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I got home and started browsing S5 cars on Craigslist. There are two near me for $15-17k with 75,000 miles.