Car too weak to redline in 1st, but idles fine. Wtf?

[ROLLingKING]

what exactly was changed last spring. etc does not equal the same tune up as another persons.lol idk much about working on an ix but i may be able to suggest something if i know what hasnt been swapped

hope it gets fixed soon. no powa is no fun!

[russhixmo]

My e28 did the same thing but it wouldn't rev past 4k. Mite be a clogged cat 😱

[Earendil]

Check the WOT switch in the TPS.

What would I be looking for? My understanding of the m20 TPS is that it has three positions, closed, WOT, and "in between". If it were getting a constant closed signal could that really keep it from reaching redline in 1st?

At least that's a test I can do from inside the car! Thanks!

[jlevie]

Check the WOT switch in the TPS.

[Earendil]

A friend just swung by with his 91 ix. He says he's had massive power loss, and doesn't think the car can even redline. So I take it for a spin, and here is what I know:

Car idles fine
Car starts up fine
Car functions the same, hot or cold.
When at idle, exhaust doesn't smell like gas (ie normal).
Car feels "okay" at lower RPMs. Not amazing, but passable for a heavy ass stock ix.
Car can NOT reach red line on a flat road in first gear. As the RPMs rise, power smoothly drops completely off a cliff.
There is no hesitation, no dead spots. The car runs smooth.
The engine still sounds "off", especially as the RPMs rise, but it doesn't feel like a car with 3 spark plugs pulled.

Of note, routine+ maintenance was done last spring. plugs, all filters, etc.

So what do you guys thing? Fuel starvation? Could the spark be failing under heavy (high RPM) load? I've never heard of or experienced an issue like this before.

When he brought it by it was dark. Saturday I'll go by his place and see what I can do. But I want to be armed with as much info and trouble shooting techniques as I can get, because neither of us has a garage, and we have highs in the 30s, and lows on the 20s these days. I can bring my fuel pressure gauge, but that's one of those tests I'd rather not do if you guys can help me avoid it!

Thanks for any help!

Cheers!
(sorry for any typos. Written on my phone)