Dead end...please help!

[mit6725]

To start with this is my first post and any help would be greatly appreciated.I have a 1999 Boxster 986 with the 2.5 litre 5 speed manual that I purchased in June of 2008 and has been a joy to own...until now! Last Thursday I brought my car into my dealership (I am a General Manager of a car dealership...another brand) to get it checked out before winter. My technician did an oil change, checked the anti-freeze and changed the air filter. I purchased the OEM oil filter and air filter from Suncoast (great price and service) as I live in Ontario and the closest Porsche dealer is 3 hours away. The air filter that was in the car was a very dirty K&N unit of which we replaced with the factory paper unit. Otherwise everything was normal and basic. I drove the car Thursday night and all day Friday and was thrilled as the car seemed to have much more get up and go which I assumed was due to a nice clean air filter. On the Saturday morning I filled the car with super unleaded fuel and tightened the new gas cap (replaced in July at a Porsche dealership due to a campaign) with many clicks as required and drove a short distance to work. Later in the day I was heading out of town and as I started on the highway the CEL came on (not flashing) so I went home (while taking it home it seemed to be running great) parked the car in the garage and took my other one on the trip. On Monday I drove the car to work (ran great) for my tech to check. He put on our scan tool and a P1128 code came up which we cleared. The car was still running great. That night as I drove it home from work it started to run rough and the CEL came back on. So the next morning I decided to bring back to work for my tech to look at again and as I started to drive the CEL started to flash so I turned around and brought it home. Later in the afternoon my tech and I drove over to my garage to see what was up with the car. He removed the MAS and cleaned it (visually it looked great...nice and clean, no issues). Then hooked up the scan tool and ran the diagnostics. It was running very rough as it was in the morning and the night before. The codes were P1319, P1313, P1315, P0300, P0301 and P0303. He was befuddled how changing an air filter and doing an oil change to a car that was running great could alter it so drastically. It makes no sense. We left the car as it was with my tech going home for the weekend to investigate on the internet and see it he can find an answer. Sorry for writing a book but I thought to get the right help you need the whole story. Any help would be great...Thanks.