89 RS 2.8L needs lots of help

[89RSbeater]

I'm posting for a friend whose 89 Camaro RS with the 2.8L is running really rough and has very little power. The odometer reads 79,XXX but it probably rolled over. He's trying to get it to pass smog, but it failed last time in the function test, i think, and the HC part.
At idle (~700rpm) oil pressure is around 5psi indicated on the stock gauge, which seems low but it will come up to normal when it's driving. Also, when revving it seems to rev up slow. And driving it, it's got very little power and seems to be jerky when shifting (it's the car, not me). Around 3000 there's a huge drop in the power band then power starts to come back at 4500. I've never driven another RS camaro, but I'd say that's not right.
We checked the trouble codes and pulled a 23. Chiltons manual said it's a MAT sensor indicating LOW TEMP. We went to the auto parts store and got a new Manifold Air Temp sensor. We cleared the computer codes then drove it and got the same code 23. Also checked timing and made sure it was at 10* as opposed to the 0* that was on the hood. At 0* it ran very rough.
My friend's taken it into a shop so many times but they never get it right. There's no vacuum leaks that I could find. Basically we need to find out exactly what a code 23 means and what it's effects are. Also what would cause it to run rough. My friend said a mechanic checked compression and one cylinder was at 80% compression. Perhaps that's the problem. He's gotta try and smog it soon so I gave him my almost new cat I took off my car right after it smogged .

I appreciate the help, guys.

[Genopsyde]

23 Manifold Air Temperature (MAT) Sensor - signal voltage is low
OR Throttle Position Sensor (TPS) error

[89IROC&RS]

well, i would say right off the bat that the cylender with low compression is the problem. its either blown rings, or a burned valve. causing poor cumbutsion, and therefore high HC in the exhaust (unburned fuel) and the rough running and loss of power. think of it as running the engine with a plug wire off. as far as the code, check the wiring from the MAT to the PCM, somewhere in between there must be a short or wire rubthrough. check the terminals for corrosion and/or burned terminals. although, if it is also a TPS sensor malfunction, it would cause the same problems listed. so the two of them together are probly makeing each other worse. i would look into fixing the cylender problem first, then look at the wiring, and then look at the TPS system. you might need a new TPS sensor.

[Genopsyde]

yea, that too

[Vlad_Tepes]

What no blower on it? Gen your gettinf slack bro

[Genopsyde]

nah, that's only when they ask how to make more power.

[89RSbeater]

I haven't checked compression yet myself, so I'm not positive. I don't like the idea, tho. Obviously that *should* be fixed if that's the problem, but the car has a salvage title so it wouldn't be worth it. I'll check compression myself and see how it looks.
A friend of mine suggested that this could be ignition related. Either in the distributor itself (cap/rotor/wires) or ignition module. Does that sound relevant here or am I beating around the bush?
The car is pretty beat up, but I hate to see my friend spending hundreds of dollars at shops for stuff I could do pretty much for free.

[89IROC&RS]

oh man, sorry, for some reason i thought you had already done a tune - up, a burned wire, crossed wires, bad plugs, fouled cap and rotor could all contribute to the problem, so a tuen up would probly be a very easy way to see if you can fix it. set the timing and everything too. make sure you undo the timing connector and set it to 0 degrees. you might have some burned wires or something, but i still stand by the idea that the low compression cylender is your problem, sorry. you could also have dirty injectors, so your friend is not completely far off. if it werent for that cyelender running low compression, i would also lean toward fuel and spark, but with that dead cylender, the other problems are not very important.