Rough Running 1999 Boxster

[mnc-i]

Fellow Forum Members,

1. I seek your guidance before I take my Boxster to an independent shop or the dealer.

2. I have a 99 Tipronic Boxster. It has approximately 207,100 miles. I changed the spark plugs, oil & filter at approximately 200,496 miles (on 1 Dec 13).

3. On 20 Feb 14, I had an independent shop replace the transmission filter, gasket and fluid. The mechanic hooked up a scanner and the following codes came up:
P1126 - Oxygen sensing adaptation frau bank 1 lower load range
P1124 - Please refer to vehicle service manual
P0446 - Please refer to vehicle service manual
P0455 - Evaporative emission system leak detected (large leak)
Check engine light is on.

4. After coming off the highway (65 mile trip from Temple to Austin) my car cut off while I was at a stop light. I had no problems on the highway (60 to 80 mph). It cut off on me two additional times on the way home. It also ran very rough, as if it was not firing on one or more cylinders. As I drove into my garage it shut off again.

5. The car left a distinct smell of a just fired cap gun.

6. I am thinking that one or more of my coil-packs are bad. The coils on the car have never been changed. When I changed the spark plugs, I did not see any damage (cracks, etc.) on any of the coils.

7. What do you all think is my problem?

Any assistance is greatly appreciated.

Thanks

MNC-I