I do not think that the low oil pressure light is a problem. I have stalled my car a couple of times due to not enough revs and the oil pressure light came on.

Don't worry about the low oil pressure warning, that would have been a result of the engine stalling.

The fault code will have been stored even though the light has gone out.

Received scanner, plugged it in (meanwhile the light has come on again, I suppose another issue has surfaced):

Only 1 code:
P0170 Fuel trim malfunction (bank 1)

For I/M readiness status, it lists catalyst monitor, O2 sensors monitor and O2 sensor heater monitor as "not completed diagnostic testing"

My next question now is: what do I need to check now in order to resolve these issues?

Each of the above issues are lambda sensor faults. Maybe try a different lambda sensor in the IM.



TC

I don't have experience of the 1.8 engine but I see that P0170 does not appear in the RAVE list of fault codes produced by the MEMS3 engine management. Are you sure that this is the correct code? Your description is close to P0130.

Secondly a member with a 1.8T recently reported non-starting with the 'check engine' light illuminating. This turned out to be linked to incorrect fuel pressure from the filter. I wonder if it would be wise to check the installation of your new 'O' ring and the security of the orange clip.

Simon

Lambda sensor ordered, will let you know how it goes.
As for the fault code, the device did read P0170, but in the meantime, the check engine light's gone out again. I scanned the car again and the P0170 is now gone, without me doing anything. I did not clear any codes.
Checked the O-ring and clip, those are both still as they should be, as far as I can tell. The car still runs normally, just occasionally runs "short of breath" at times which does seem symptomatic for a lambda sensor problem