Code 23 - what now?

I tried to do diligence and search the site but haven't found a viable solution to my woes. I have a 93 RRC LWB with 83K and yesterday it was stalling out at stoplights when warm. Today same thing, then at one light the RPM hopped around with no gas pedal pressure and then stalled out with a check engine and code 23. I know the code is a fuel pressure system issue. But what is the Test 20 of the continuity test? I also tried to clear the code about 5 times with no luck, so I need to attempt a remedy - as usual, I appreciate the experienced genius of this forum.

Are there "ususal suspects" in a code 23? Another site mentioned fuel filter which I thought the PO did, but going thru the receipts, I confused it with them replacing the fuel pump relay. It appears this was happening often as of late for the PO. Here's a brief look at what the PO had done via receipts.
Current milage = 83K
75.2K - Stalling reported at stops PCV system cleaned T and Flame trap. Tune up as well - plugs, wires, cap, rotor.
75.7K - Highway driving car will want to stall at stop. Vehicle Speed Sensor installed could not duplicate the stall.
79K - Vehicle towed in, would not start - Diagnosed fuel pump relay and replaced
20 miles later... Vehicle not idling correctly, tach bouncing at stop - replaced intake manifold gasket, end seals, valve cover gaskets, reset engine adaptions.
My purchase @ 82.8K - Installed Borla exhaust, Cat back.
I'm no mechanic by any means but it seems like there's no mention of any codes being thrown or they didn't note them and they're just tossing parts at it. Am I correct?
Could this be a simple Fuel filter issue? I guess it could use replacing anyway. Additional thoughts in light of the above?...

Have you cleaned the IACV and its orifice?
Also check the pressure at the fuel pressure valve on the return line to the fuel tank.

Thanks Les,

Two dumb questions. What/where is IACV and how do I check the pressure or is this a tech's job?

IACV aka as the stepper motor. It's the big round sensor that screws into the right side of the plenum towards the back. Disconnect the battery, unplug the wiring from the sensor, take a large adjustable wrench and unscrew the sensor from the plenum. Clean both the tip of the sensor and use carb cleaner to clean the inside of the plenum where the sensor was screwed in. Reinstall and reconnect the battery.

I didn't see stepper motor on any of the paper work. Guess that was an oversight when doing the T and Flame trap. I will give it a through cleaning.

I'm having the same issues ! How did the clean go ? I pulled the stepper motor, cleaned it, used carb cleaner on the inside, cleaned it out as best I could and then started to get a code 48 on the OSD screen under the passanger seat :(

I would also like to hear how this turned out because I am having a similar problem with a surging idle at stop with it wanting to stall occasionally. I don't have any codes though.

OK Tomorrow is Rover day. Picking up another Classic for some body parts and then getting down to this code 48 issue. First thing I'm going to try is a re-clean but also a fuel filter change to see if that solves the idle issue too.

I'll keep you updated.