I bought the car in March of this year. The intake was installed 2 owners ago, a couple years ago. I'm friends with the last owner, and knew about the car and that the SES light was on most of the time. I was told it was "because the MAF is a 78 and the intake/tb is an 85 and it just needs tuned." I don't so much believe that now...

I've fixed multiple broken vacuum lines/connectors, and it does pass smoke tests (I haven't seen it though).
New sensors: MAP, IAT, ECT, front o2's (the rears do appear to be working, as they respond to accelerating and drop to 1-200mv). New PCV valve, new plugs/wires, new paper air filter. MAF is clean, and I have not run a K/N filter (previous owner did). Multiple mechanics have commented on how strong it sounds, and I would agree.

My problems never surfaced until this glorious 100+ Arizona summer hit. It still runs great in the mornings, although the fuel trims and such are no different (minus the oil pressure thing). I'm thinking the guys who installed the intake suck at it, or perhaps my PCV hose is bad somewhere but I've checked it. It is pretty oily in there, though I hear that's common. The car does use about a quart every couple months (no leaks on pavement), and the oil looks fine.

Thinking about going to 5W-40 to help with the heat and see if that does anything. Could I possibly have a failed oil pump o-ring? Doesn't really explain the rattle though, and the Torque knock-test actually showed no knocks. Don't know how reliable that is.

 

The fact you lose oil pressure after the car goes into closed look is odd to me. Oil pressure is "mechanical" with a pickup tube connected to a pump. The gauge on the other hand being electrical could be causing you problems. Keep in mind, oil will become less viscous as it warms up. It's common to idle at 30psi cold and maybe 15psi when warm.

If you have an upgraded MAF and intake and NO tune then that's not right either...You allowing more air into the engine and the car is programmed to only allow a certain amount of fuel to compensate.

If you are confident you have all the vacuum leaks fixed and all sensors are OK, you MAY be down to either putting a stock intake on it and see what happens or getting a tune. Neither one will be "cheap" since both of them may be couple hundred dollars.

 

I'm hoping that moving to a little thicker oil will help with the heat conditions. I never had these issues until it got over 100 degrees outside, so I hope its something that simple. According to the gauge I have more than enough pressure when hot (30 psi idle, ~50 when accelerating, down 10-15 psi from when it's cold), but since it's jumpy when hot I don't really trust it. I almost think the pressure is way lower than indicated and the gauge "catches up."

The MAF is stock, it's the T/B and intake are bigger. I've talked to a couple different tuners and while they said it's not optimal without a tune, there's no way that should cause a lean code. Getting it tuned was first on my list but the guys I talked to both said I should make sure I don't have other issues causing the code first. Glad I did! I'm going to pull the intake soon, look it over, and reinstall it with new gaskets. I really think that that is the root of my problems.

I don't think I ever mentioned this, but it has always idled great. No surging or roughness at all, cold or hot.

 

My previous 99 cobra had similar issue with both banks reading lean. Ended up being a vacuum leak that would rear its ugly head when up to temp or when the intake with warm up and expand. It was a 2 pc aluminum factory intake and the top "lid" gasket was the culprit.after I chased it for 2 weeks using a data logger etc and ended up that I simply removed the upper lod and added some black hi temp silicone in addition to the gasket. Problem solved.

You may find your issue, but you can't really add silicone like I did. LS intake manifolds usually use simple runner gaskets. At least my factory LS1 GTO intake did.

I would get a vacuum diagram for the engine and trace/remove EVERY hose that flows air through it.

 

My previous 99 cobra had similar issue with both banks reading lean. Ended up being a vacuum leak that would rear its ugly head when up to temp or when the intake with warm up and expand. It was a 2 pc aluminum factory intake and the top "lid" gasket was the culprit.after I chased it for 2 weeks using a data logger etc and ended up that I simply removed the upper lod and added some black hi temp silicone in addition to the gasket. Problem solved.

You may find your issue, but you can't really add silicone like I did. LS intake manifolds usually use simple runner gaskets. At least my factory LS1 GTO intake did.

I would get a vacuum diagram for the engine and trace/remove EVERY hose that flows air through it.