I am having exactly the same problems with my 03 LAG II DCi 1.9 120 Expression.
Intermittent check injection warning lights and loss of power as it goes into limp mode. Over the last month or so, I have been noting when this happens and it is completely random. Engine cold, or warm, under acceleration, at cruise on the motorway or even on back roads at below 60kph. Full fuel load, and tank near empty, it makes no difference. So, I am thinking dodgy sensor.
I have previously cleaned the
valve and the solenoid appears to be OK. I have also cleaned the
filament with electrical contact leaner and checked every sensor for faulty wiring, to no avail.
boosts well in the expected range and on long runs in sixth gear at 100kph, it returns 65mpg according to the gauge, so I don't think there's a fundamental problem with the engine,
I have not managed to connect it to a diagnostic just yet, but reckon I'll start trying to isolate this. Can I just run it without the mass air pressure sensor connected and see what happens?
And what about the waste gate solenoid? How does on test that properly?