[Lotus]

if the oil level is OK, temps are in check and you still get that behaviour, then something is bleeding off the oil pressure.
At worst it could be a rod bearing on its way out. One of the first systems is loss of oil pressure at idle from the increased clearance.

 

[Lotus]

if the oil level is OK, then an oil pressure gauge will tell you more, .i.e. if it is really low.
If you need to drive it, consider running a 50wt oil and don't push the engine load- and rpm-wise.
If the light is off with the 50wt oil, e.g. a 20W50, then you are internally losing pressure.

 

[Lotus]

not a good idea as the plugs and internals of the sensor are made from plastics.