Reduced Engine Performance inconsistency (2005 XC90 2.5L)

[ArrowNought]

TL;DR
Limp mode turns on when turning on car after being off for >~3 hours, but turns off if I turn car off then back on again. Any ideas why?


A couple weeks ago, the check engine light came on and I didn't have much time to look into it. After a couple days, it went away. A couple days after that happened, I go to start my car and the "Reduced Engine Performance" message pops up and I decide to not drive it around. Check the OBDII code and the only one was P0496.

I saw somewhere that a bad engine air filter might be a potential cause for the limp mode, and I had one on hand, so I swapped to a new one. That did not fix the problem. After checking on it for the next couple of days while constantly looking for forum posts about what issues might have caused it, another message popped up, "Engine System Service Required".

At this point I started thinking about stuff that my engine might be bad on. I recently had a maintenance with a 3rd party mechanic who resolved my engine misfiring on hard acceleration. I also noticed that my car was almost due for an oil change. I pull out the dip stick and I was missing a LOT of oil. Bought the same oil that I already have in my car and filled it to about 75% on the dip stick. I reset the codes to drive a tiny bit out of limp mode. I do this every day, drive a little bit and check the oil.

Eventually the Engine Service message goes away. And one day the Reduced Engine Performance goes away on its own about 30 seconds after turning on the car. The next day, no message at all! But then, every day since then, when I start the car cold (~3 hours of cool down time needed), limp mode comes back! I can get it to go away by turning the car off then back on again, the code just goes away after 5 or so seconds after turning it on the second time. The only code that still pops up is the P0496 with my OBDII tool.

I scheduled an oil change and a search for an oil leak at a local auto shop next week (earliest I could get) but in the meantime I thought I'd look for any insight here. Thanks in advance!