Rep Power: 0

Background:
I have a 2002 Honda Civic (220,000 mi.) that threw a CEL last week. Code was P0171. The car has been with the D17A, JDM engine for more than a year and has ran fine since.

Parts:
I have replaced both oxygen sensors, replaced spark plugs and cleaned out the MAP sensor this week. Fuel pump was replaced last year. Cat was replaced about 40,000 miles ago.

Numbers:
My short term fuel trims are high at idle and climb, especially when I give and hold throttle but drop immediately to 0 when I release it. Then it climbs back. It eventually reaches the limit of 46.9 and just stays there (with or without throttle). Obviously my long term fuel trim levels are high as well but I have disconnected my battery a few times the numbers get erased. When I connect a vacuum gauge to the throttle body I get a readings around 20 in.HG at idle. However, the needle bounces around rapidly while staying about 1 +/- from 20 in.Hg.

Thoughts:
Because my STFT levels climb when I give throttle and because of the vacuum readings, I'm lead to believe that this is not vacuum leak related and rather an ignition issue. I do not think this car has had the valves adjusted in a long time (if at all) so I'm open to it being a valve issue as well. This is a suggestion I've come across so I am open to that as well.

HELP:
I'm curious if anyone has suggestions at what I should be looking at or if I'm forgetting something here. I have very little money for a shop but enough to buy some parts and feel comfortable to do most work myself (unless I have to remove the head). Any help is really really appreciated. I'm up for smog soon so I'm kind of stressing here hahaha

I am looking for valve specs before I remove my valve cover to see my spacing with a feeler gauge.

 
Rep Power: 0

Update and also a plead for help:

I cleaned the throttle body of any deposits that had built up. Tested fuel injectors and coils. Didn't have specs but all tested within the same range of each other so I'm going to assume they are fine? I cleaned all sensors attached to throttle body as well and re-checked vacuum hoses. Still have a jumping vacuum gauge.

This is where it gets juicy, I let the car sit and idle for about 5-10 minutes after all that and it threw P0131. I got this code last week but thought changing the O2 sensors resolved the code. I drove it around the block after resetting the code and if I floor it from a stop, the car feels like it loses power and lags. It accelerates after a second or two. If I do this while cruising, the car lags but doesn't feel like it loses power to the same extend as when it is from a stop. I still have high fuel trim levels as well. Please, any help or thoughts as to what direction to take this would be really helpful. I am on day 3 of this and I'm beginning to feel worn out by it.

I guess the TL;DR is:
high fuel trim levels at idle that climb with throttle
loss of power if floored from stop
rapidly bouncing pressure gauge at idle but within ranges
P071 AND P0131
Have replaced spark plugs and O2 sensors recently with OE replacements

 
Rep Power: 231

Sounds like a fuel delivery problem. Check fuel pressure at idle and at 2500 RPM.

 
Rep Power: 0

THANK YOU FOR RESPONDING. You have no idea how hopeless I've felt. No forum I've gone to has gotten much traction. I'm determined to find the issue though so I just need a little help along the way.

I am trying to test the fuel pressure at the moment. I'm not not sure how to depressurize the fuel line before I start taking the fuel line off. Any clue?

I found a 15A fuse in the internal fuse box that the diagram reads as "Fuel Pump." Is that the right one? The Haynes Manual I have doesn't really help with this step and I don't want to just assume that the 15A relay is the one I am looking for and then have to deal with gas spraying everywhere lol.

 
Rep Power: 0

Tested fuel pressure. Took me awhile to figure the clips out but I got them off eventually haha

Ignition on, engine off: 8 PSI(not sure if this number matters)
Ignition on, engine on at idle: 24 PSI
Ignition on, engine on at 2500 RPM: 24 PSI
Spec per Haynes Manual is 40-47 PSI

I did replace the filter last year. It was a random one I got from Amazon that was inexpensive. I'm guessing it's clogged/bad. If so, no biggie. I'll be taking it out tomorrow to inspect. Anything else I should look at/for?

I have a multimeter, vac pump, and pressure gauge to measure anything. I'd rather not throw parts at it but I realize the car is old so I'm open to the idea that I might need to replace the fuel filter/pump.