Low oil pressure light flashes at idle when the engine is warm. It doesn't do that when the engine is cold and it flashes more frequently the warmer the engine gets. The light doesn't flash or isn't on under load. Oil level is halfway between min and max. I don't see signs of coolant and oil mixing. No obvious signs of leaks and oil level is constant.
The car has another issue as well: lean at idle. STFT values at idle are extremely high, topping at 25%, LTFT is approx 13.5%. Sometimes the ECU goes to "open (?) loop, failure" mode with predfined rich fuel trimms. Oil smells at least some fuel but not more than two years ago. No smoke coming out of tailpipe when the engine is warm.
I know that lean idle should be addressed but the only DTC has been P2187 which to me seems like an expensive diagnosis as I don't have the skills to do it and don't know any mechanics that I could trust to not start the "let's swap some parts" roulette. Besides the problem only manifests at cold weather. The car also has another probably expensive defect, 5th gear is popping out while driving (no leaks, oil change performed approx 50000 km ago), so I'm not willing to spend hundreds of euros on it.
The oil has been changed 9 months and approx 7000 kilometers ago. For the last two months there has been quite a lot short running and idling and I was forced to idle for an hour due traffic accident in minus 25 Celsius weather.
My question is, can the oil be so badly diluted with fuel that it lowers the oil pressure so much that the pressure is below the minimum for oil pressure switch to trigger? Would it be worth to try to change the oil and use thicker viscosity?
The oil is 5W-30 synthetic, the thinnest that manufacturer recommends. The oil pressure light is on while ignition on and engine off so doesn't that indicate that the switch is probably functioning correctly?
The car is Mazda 3 1,6 L gasoline engine with approx 156000 kilometers on it. There might have been a period approx four to seven years ago that no oil service and proper driving took place. There's no receipt or such to indicate that oil has been changed during that time. Since 2021 the oil has been changed on yearly basis, under 10000 km intervals.
Is it paint to get to the oil pressure switch to measure pressure and change the switch if needed considering this car model and the fact that the splash shield bolts and such are probably badly rusted?
EDIT: The engine makes ticking sound at idle which removes under load but it's been like that since I bought it so I've thought that is normal for it.
EDIT2: Car is from 2005. No timing chain or oil pump maintenance performed.
