p0122, car wont start

I have a 1999 Chevy suburban, 1500, 4wd, 5.7 gas engine. 150,000 miles.
wednesday it drove perfectly. thursday it will not quite start. i say "not quite" because it catches and starts, but stalls immediately when you release the key. fuel pump appears to be working normally. obd reported a p0122 code. replaced the TPS, no change at all. haynes manual said to test the voltage going into the tps. basically it shows NO voltage. that would seem to indicate either a loose/damaged wire, or a computer problem. Anyone have any ideas to figure out which? where does that wire run to?
any help is appreciated.
if i have totally missed the point of this site,, i apologize in advance.
thanks
mike

no guesses???

Sometimes you have to be patient till someone gets on who can help. Did you properly adjust the new tps? Make sure. If problem persists, check for throttle position signal at the blue wire. On a scope, it should be a smooth line that goes up with throttle given and down when released with no drop outs. You can also use a voltmeter, but it won't show if there are any dropouts, but it will tell you if theres a signal coming out of the TPS. If there isn't then make sure there's 5 volts on the gray wire (key on engine off). If you don't have 5V reference on the gray wire, you need to find out if there's a break in the wire, or where the 5V ref is lost.

i definitely didnt adjust the tps. i just swapped the new one for the old one. the haynes manual said to check for 5v at the gray wire with the ignition key ON. in any case, there is no voltage to the gray wire. i found a gray wire going into the ecm/pcm on the clip. i checked the wire for continuity with the gray wire at the tps. it showed that the wire was good. i checked the pin on the computer for 5v and got nothing. my guess is the computer is bad?

Not necessarily. First, continuity tests aren't conclusive with the PCM plugged in because often drivers share a ground, sometimes different capacitors share grounds. IT's just not conclusive. Secondly, it's possible that another sensor is shorting out the 5V ref. circuit. To tell for sure, you can remove the 5v wire from the PCM (remember there may be more than one grey wire. You'll need to get a pin # and make sure it's the 5V ref wire) and check with Key on, engine off for 5V at the pin. This will eliminate the possibility of another sensor shorting out the ref. voltage. If there is 5v onthe pin with the wire removed(or cut) then there's a short down the line somewhere. If not, then condemn the computer ONLY after checking ALL powers and grounds to it.

I dont have a wiring diagram in front of me but usually that 5v reference should be shared by other sensors like the map sensor if so then the driver in the pcm should be ok or you would have multiple DTC's. Are you sure you are getting a good connection with the DVOM? Did you check the ground?

hmm. no i didnt check the actual ground for the tps. when i checked the pin from the pcm, i went directly to ground on the frame with the meter. it showed nothing. after work today i am going to check the grounds and every other connection i can get my hands on....i will report back....
thanks guys!

ok, i am an idiot.
the voltmeter was set to AC instead of DC. now all my voltages read exactly what the manual says they should read..... i'm sort of stumped....

Well go back to the tps adjustment. Did you do that or is there even an adjustment? Should be somewhere around .45V at closed throttle. Does the new tps have a good signal out?

there is no adjustment i can see. it just slides over and screws onto the side of the throttle body where the pivot shaft sticks out.
i will check the reading out of the tps tonite..

just a thot i wondered if anyone had input on. i got a pcm flashed to my VIN. it came with instructions on how to reset the password for the anti theft system. it mentioned that the car will start and then stall until the password is set.
that made me remember that the "security" light had been on intermittently for a while now. i had no clue what the security light meant, so i didnt worry about it. could a problem with the anti theft system cause the car to act this way?

yes it can, did you follow the instructions on how to relearn the key?

not yet. i had left hood open slightly and light ran the battery down. so its charging.....
i have not installed the pcm yet. is it worth trying to do the password reset before i install it?

wow.
that did it. a few turns of the key and 30 minutes later, the engine is running fine. no new computer no nothing.
Now my question is, what causes that and how do i prevent it happening in the future?
thanks a bunch for all the help!