ERROR CODE 23 & 87

1990 LTC 150Kmi. Started to occasionally stall while in Park close to a year ago. About two months ago it started stalling more often and shortly after starting engine. The past two weeks just kept getting worse. It will not run at idle smoothly or while holding throttle steady at highway speed. ERROR CODE 23 is: Throttle Position sensor out of range. ERROR CODE 87 is: Primary Fuel Pump circuit failure. I understand the code 23 but, the code 87 could mean anything. Is there anyway to pinpoint what the problem is. I cannot find any info on this code. I have a shop manual and I can't find it anywhere. I've gone through the troubleshooting checklist at the front of the manual and it just makes everything kinda blend together and then it seems that everything needs to be replaced. I checked the EGR valve and it looks to be operating correctly. Fuel pressure is around 32 p.s.i.. I just bought a fuel filter and fuel injector cleaner will install tomorrow. Any help on this matter will be greatly appreciated. Oh, one other thing. When I press the accelerator pedal to the floor it just flattens out. It accelerates but barely. During this, the CHECK ENGINE light comes on and then goes away shortly after releasing the pedal. Thanks again.

OK. I've changed the fuel filter. I do have about 8 P.S.I. more now on the fuel rail. Still have the rough idle though. I started pulling vacuum lines and when I pulled the line going to the M.A.P. sensor it leveled out and started running smoothly. I thought this is great. The M.A.P. sensor is bad. Then I thought, well, I have no codes showing for the M.A.P. sensor. So, now what do I do. Should I waste $50 on a new sensor or is there another problem?

Unfortunately..... yes.
It might be cheaper to sub junkyard parts during this stage of the game.

I don't see a MAP Sensor test procedure in my book.

It's fixed...friend has a '90 Bronco and I swapped out his M.A.P. sensor with mine and it ran great. So, never trust a computer.