Here’s some back story on the car, it was advertised as having no check engine lights despite having sat undriven for one year. I drove out to pick it up, and on my drive home I had the check engine light come on. The codes were P0026 & P0027 (intake valve control solenoid range/performance bank 1 & exhaust valve control solenoid range/performance bank 1), however after clearing the codes it didn’t seem like as big of an issue. The main problem I faced was the fact that I got a flickering low oil pressure message & oil light after about 30 minutes of driving.
I did some research and decided to call back the owner and ask him a few questions. I learned that the oil had not been changed for almost 3 years, and the car had only been driven intermittently for a few long road trips about 300 km maybe five or six times total. He was unfamiliar with the engine lights that I described to him.
I decided to take action into my own hands and did a full oil & Filter change using a cheap Kleen Flow product to flush out the old engine oil before replacing it with new oil. Despite the oil change the oil pressure light came on within 15 minutes of driving the car. Please note that while driving it will flicker on and off depending on the load given to the engine, it almost seems electrical but I will get to this later. I continue to do lots of research on different forums and discovered if there’s only a few issues that could possibly cause that light. The first thing I did was to replace the oil pressure switch, this did not solve the issue. Following this I flushed the old oil with LiquiMoly Engine Flush, replaced the entire PCV system with every single pipe and hose possible (there didn’t seem to be any clogging in the old system). I also simultaneously replaced all of the seals in the oil pan including the one for the oil to pick up tube (Metal) {I did not remove the mesh as it seemed to be in good condition}. There was no evidence of any bearing damage in the oil pan, however there was quite a large amount of sludge in the form of medium/large black chunks and lots of finer particles. I cleaned out the pan with brake cleaner and compressed air before reinstallation, however it was not perfectly clean.
Once everything was reassembled I test drove the car and within 10 minutes the light began to flicker again. If I turn off the engine and start it again there is no evidence of a light, and I can drive it relatively gently without the light coming on. It’s only when I do a pull that the light flickers on. Another small detail which I noticed is that prior to changing the oil pan seals, the message was “low oil pressure…” and now it is “no oil pressure…” however the spontaneity of this message is exactly the same as before and this is only a minor detail to me.
I am wondering if anyone else has ever had a similar experience to me on their P2 Volvo and If they had any advice that they could share. Essentially I am asking for help to find the next step to solve this problem. I will be very active on the forums for the next week and have also attached some photos from the work I’ve done so far. Any help will be greatly appreciated. 
