Vauxhall Corsa Running Rich.(see description)

this Corsa failed the emissions test during the MOT, the CO% was 5% at idle.
there was no fault codes, so I looked at live data to see what was wrong.
the fuel trims were taking away fuel but the front O2 sensor stayed rich at idle.
I looked at the fueling inputs, MAP and TP, this car has not got MAF
the MAP stayed at 1bar all the time, this wasn't right, it indicates an atmospheric pressure in the intake manifold that can only be achieved with a fully open throttle.
this is why I checked the throttle on the live data. it was working fine.
then I checked the MAP signal voltage on the scanner, this was changing as you would expect. the thing is the MAP pressure on the scan tool didn't change. resulting in too much fuel being delivered.
At this point I knew I had a faulty PCM and I hadn't left the driver's seat.
The testing on the engine was just showing other ways to prove a faulty PCM to back up the driver's seat diagnostics, because the test may seem too easy, and a PCM won't be a cheap fix.
Test light to show the wire to the PCM was ok.
The hose on the MAP sensor to show the sensor itself was ok,
The vacuum gauge to show there wasn't a massive intake leak, it was ok.
I reflowed the solder inside the PCM due to its location on the engine (getting extreme hot and cold conditions isn't ideal)
luckily for the customer this fixed the PCM,
although the driver's seat diagnostics was still correct.
Thanks for watching.