Oil pressure flickering with P0441 code

So, I had two problems apparently happen at once and don't know if they're related. I took my 07 Galant 2.4L on about an hour long ride after it had been sitting for several months. I ran it to charge the battery and left the next day. After my drive I noticed the oil light flickering at idle. Then it started surging and stalling and was hard starting, and the CEL was on.

I changed the vapor solenoid on the side of the engine and it took care of the idle problems and CEL but the oil light remained.

I then replaced the oil sender on the other side of the engine. No change. I also changed oil. I always use AmsOil.

So here are the facts:

I have to drive it at highway speeds for about ten minutes before it lights up.
I can idle for a very long time and as long as it isn't driven, it wont do it.
If the light is flickering/on and I shut it off for 5 mins+ it stays off until driven.
Only turns on in RPM range low idle-900.
Throttle body appears to be really clean, no residue on intake tubes or where they meet the TB.
I can't put a guage on it because I have to take everything apart to screw one in, and it would cool down too much by the time I got it all back together.

What are my next steps here? I'm lost now, and this seriously is the ONLY mechanical problem I've had with this car since I bought it on Black Friday in 2010!

Any help is really much appreciated.
Chris

This may sound completely counter-intuitive, but have you tested the battery and alternator? If not, do so, because improper voltage can not only cause the idling issues you had, but cause a Check Engine Light also. Our cars have a learning system for the engine and transmission. It is designed to adapt to a person's driving habits. When the battery is drained, that programming is essentially forgot by the vehicle and it must re-learn everything.

Thanks for the reply. Yeah, all that is good. Actually, the idle and CEL are both back to normal after I replaced that vapor solenoid. I had originally thought that the super low idle was causing the oil light to flicker, but it still happened after that. I just mentioned the idle issue even though that part is fixed only because I thought it was a heck of a coincidence that both problems popped up at the same time.