[Stevetwood]

@CrisZenithBlue When the CEL light was on, the car was running okay (ish) although the fuel economy was very poor, at about 23 mpg on Shell 98 RON fuel (No ethanol). Now the fuel economy is 28-30 mpg on the same fuel and my son has taken the car to France this week an told me yesterday getting an average 36 mpg driving at around 80 mph (with the customary toll-booth drag race at each booth) for over 180 miles on their freeways. The car has done nearly 3,000 miles now and the CEL has stayed off. So now working the problem in my head (beware, these could be the ramblings of an idiot), I think that the MAF was dirty and needed cleaning because the previous owner allowed the mechanic to replace the air filter with a poor fitting non-Porsche air filter that allowed dirty air to enter the system which soiled the MAF sensors which was unable to measure the correct quantity of air value (I cleaned the MAF twice and had a P1128 value and a pending P1130 value between the two cleans which I cleared down, then I fitted the new Porsche air filter when I cleaned the MAF for the second time). The O2 sensors were reading a high O2 value because of the air filter vacuum leak causing the ECU to squirt more fuel into the system leading to poor fuel economy.

@100deltacharlie - as was said here earlier by @Burg Boxster O2 sensors don't tend to go in pairs and throwing a couple of hundred $ at replacing them is not always the answer. A good mechanic will try to work the problem and not just change the suggested faulty parts. I got the code reader from Amazon search for "U480 CAN-Bus OBDII OBD2 EOBD Trouble Code Read Diagnose Tester Diagnostic Scanner" and it was closer to $25 with postage.