no power under load + backfires - fuel pressure? ignition? sensors/ecu?

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I’m. So it’s running but when you hit the throttle it is very slow to respond and back fires, YES?
if that’s that’s the case it’s probably off one tooth on the cam timing. Many times someone will put the belt on and use the flat of the head as the mark or the belt is getting ready to snap. The timing mark is actually below the flat of the head on the passenger side. It’s a bump on the head. It the marks on the crank and cam are lined up and it’s still having problems it might be the MCA jet valves. You can check them with a vacuum gauge. When they go bad the needle is a whip.
If the timing is off 1 tooth the engine will run but but have no power. In the tech section we have pictures of the mark.
also a bad coil will keep it from revving up and can cause erratic timing

thanks camoit, this is useful as leads! i can believe that the cam timing could be an issue, but what befuddles me is that the engine was working fine for a while. then a) bad spark wire, b) busted exhaust manifold led to big problems but they kept running it. now those are fixed, but i don't see how doing the repairs on those would have affected the cam timing?? unless it slipped? or, as you say, is stretching and ready to snap?

as for the mca jet valves -- isn't that a 1st gen thing? do 2nd gen engines have them? (haynes says carbureted systems only?)

here's another weird symptom: the revving problem was getting worse and worse. got to the point that i couldn't even get it to rev in neutral, with throttle wide open. switched the MAF with that from the '96 parts car, and it worked better again -- back to the original problem, of really bad power at low RPMs. again, to describe this -- in neutral, it stutters and is slow to rev when suddenly go wide throttle, but if go slowly it revs fine. when driving, going up a hill is hard because the light touch on the accel isn't enough to really make it go. but once you get higher revs, it's pretty much fine -- except for backfires now and then, especially when releasing the throttle.

i'm going to go and test the TPS. when i disconnect it, behavior is basically the same, which i realize might be an issue. going to do the resistance test...

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well, just did the TPS test, and i don't know? haynes manual is confusing -- it says to measure between terminals 1 and 4 for base test, where i get 15k-ohms and manual says 6.5k-ohm max. then it says to measure between terminals 2 and 4 for sweep test, but on mine terminal 2 is missing? going from 1 to 3 starts at 5k-ohm at closed throttle, to 15k-ohm at wide open ... so maybe it's describing it backwards?

i suppose i could test the voltage as well, but i'm out of time.

two more notes:

1) i've previously swapped the coil with the parts car, no change. i think that rules it out?

2) i'm guessing it's not the fuel pressure, for now. i rented a fuel pressure tester, but couldn't for the life of me figure out how to attach it without the special very-hard-to-get adapter, or cutting the fuel line (ugh). also, i'm kind of assuming that since it revvs super-high when i get it going, it must be feeding the fuel pretty fast. (is that a bad assumption? is there another way to get a sense of if fuel pressure might be the problem still?)

thanks for the help everyone!

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TPS measures the same on the parts car, so I don't think it's that. Argh. How much of a PITA to open it up to check the timing belt on the cam?