Warm or cold oil light comes on when idle causing the car to stumble and shake so badly it acts as if its falling dead. It also starts up this way warm or cold. Loss of power. Example. Sometimes when pressing the gas halfway it acts as if your barely pressing the gas at all not even reving up or raising the engine up like it should, unless you nearly floor it and make it kick. Sometimes it runs like a 2.8. Its tuned up with a new oil pressure switch. I can hear a quick rattle right after the engine turns over the last time to start, but goes away quickly. Sometimes I also hear a different rattle when accelerating that gets 2x louder if I am in low gear. Not sure if its the trannie or engine. Check engine light comes on, but diagnostics only shows O2 sensor. Other than any of this, it will run good. Any idea what the problem is, or what route I should take first?

Hook a mechanical gauge to it and see what the oil pressure actually is at idle. Could be the pump is weak and ready to quit. Get back to us with a warm pressure reading.

First the stupid question, did you check your oil level? The rattle you are hearing maybe the valves starving for oil. What weight motor oil are you using? The O2 sensor will affect fuel mixture.

How many miles on it and do you have any maintenance records showing regular oil and filter changes and what kind of oil? Have you always owned it or do you know how it has been driven?