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stphnsns, To answer the rest of your questions.... Yes, I do the work myself. No dealer for 150 miles and I don't trust the local independant as he told me he didn't consider the Boxster to be a 'real' Porsche. As far as changing the O2 sensors, it is a tight fit. Probably the hardest part is connecting the wires. Have to go through the trunk to do the rear sensors and under the car for the foward two (must easier access). Yes, my car does smoke upon startup on occasion, about 5% of the time. Pretty much normal as my VW does as well from time to time.
stphnsns: No that wasn't me. If I were you I would hold off on replacing any O2 sensor. These codes are triggered by their readings and not necessarily by their malfunction. Also, hold onto your old MAF as I don't think the problem is there either. The generic error codes and some of the past advice I've received can be misleading. I just found the OBD-II codes on this site. It states that 'P0455 = Fuel Tank Ventilation System (Major Leak) - Below Lower Limit'. Also, looking through old data logs from my car I did notice I had a 'P0446 = EVAP Canister Shutoff Valve (Function) - Below
Didn't want to let this die without finding out if the problem was solved as I have and am experiencing a similar problem. I have a 99 Boxster I purchased in January of '03. I experience the P1124/1126 error codes and power loss problems. I eventually changed the MAF and all four O2 sensors with my 'shoot-from-the-hip' diagnosing over the summer. Everything seemed fine throughout winter with no CEL until the beginning of this month. Now I have on several occasions received the 1124/1126 and 1123/1125 error codes. On top of that, the car seems to have trouble starting (not all the time)