Ok so I installed the £12 upstream O2 sensor 500 miles/10 days ago. Ran my OBD2 scanner and at first it didn't report the sensor but after a run it was reading figures from it and it was passing the tests. I'm pretty sure the old cowboy garage fitted sensor never did that. Incidentally the £12 sensor head was noticeably smaller than the old one, I wonder if they just fitted a wrong sensor, maybe the downstream type.
MY OBD2 scanner gives more info than I know what to do with but I have noticed the live running page shows the O2 sensor voltages in real time and they alternate within the correct range at 2K RPM. Saves me getting my oscilloscope out.
Anyway so touch wood it is now fixed.
Only one anomaly - a brief and one-off kangaroo like loss of power 4 days after install, reported by my partner. Not occured since. No error codes reported. I took it to be either ECU adjusting to getting readings at last from the O2 sensor, spark plug issues (they had been in 40K miles, I was waiting for the O2 issue to be fixed before replacing), MAF sensor needs cleaning or EGR valve sticking. Replaced the 8 spark plugs with Iridium ones gapped to 1.04mm (bargain £52 from GSF!). Old standard NGK ones looked fine, gaps up to 1.2mm.
I plan to blank the EGR valve shortly. Is it worth cleaning the MAF sensor or better left alone?
