280z afm testing + other ?s

hey guys.
so ive been having smog problems recently. i got a tip from a smog station that my afm might be the problem b/c its running lean at idle and very high on CO at speeds above idle. so i took the afm and ran some tests w/ an ohmmeter and it failed both potentiometer tests. these 2 were from the fsm
when i ran this test (as seen on http://www.atlanticz.ca/zclub/techtips/afm/index.html):

Measure the resistance across pins 7 and 8 while moving the flap. It should change. (though it may be jumpy)

Repeat this but between pins 6 and 7 while moving the flap.

the resistance only dropped a little bit when i began pushin the flap back, but stopped dropping about a quarter of the way in. resistance went from continuty to approx. 0.4 ohms. it checked out on the rest of the tests. my mechanic friend tells me he doesnt trust ohmmeter tests b/c he's seen parts that fail resistance tests work fine, but I was thinking it would make sense that the potentiometer was bad b/c that could make the flap open, but not all the way. so at low engine speeds, it could get too much air, making it lean, and at higher speeds, too little, making it rich. is that good logic? also, it seems my car will not rev past 3500-4000 rpm, and its got a rough idle. perhaps related?

also, any ideas of what else could be causing my car to run rich would be helpful. the technician mentioned a couple things, but i didnt write them down ( i know, i should have). i think he said my cold start valve shouldnt be the problem, i didnt understand why. also, my fuel pressure is registering about 40-41 psi at idle, and jumps to about 43 when i rev it, and i know that the fuel pressure should be at about 36 psi. so im thinking about the fuel pressure regulator too. could also be that the gauge is faulty or inaccurate, it is installed on the fuel feed line, but i have heard that this doesnt indicate the "true" fuel pressure as that should be measured from the fuel rail?

also, i am in the market for an afm, and i might make a trip to see a guy with a couple of them tomorrow. he has 2 280zx afms, but only 1 280z afm, all used, not tested yet and have been tweaked for air/fuel ratio adjustment. so i was wondering do 280zx afms work in 280z's too? i know they both have l28's so they should right? but if not, i think i'll go for a remanufactured one instead off zccjdm.com.

so what do you guys think???
thank you soo much!!