Car speeding up on its own

A while back my car started speeding up by itself with foot off pedal. A week later it happened again. Started happening more often and car started stalling after just a few blocks.
I finally got around to buying a MBD-II scanner and read a P0121 code. Throttle/Pedal position sensor/switch a circuit range/performance. I also had a freeze frame P0001 code fuel volume regulator control circuit/open. I was getting a rpm's of 1700-1800 at start and idle. Throttle showed open forty percent (that is right) at start and never really went below thirty seven percent. Hitting the gas got somewhat erratic movement of throttle.
I replaced the TPS. (There is some sick locktite on those screws)
Seemed to be fine for about a week. After a week same thing happened again. What I did realize is that if I started car with air conditioner off the car would last much longer before stalling and would usually have a normal 700-800 rpm's at idle. Same problem with throttle open and stalling. I checked the throttle and was not open at idle, but still read at forty percent.
Thought I possibly got a bad TPS. Tried reading the voltage with a multi-meter. I do not know what was I was doing wrong but I could not get any reading at all, not even on the battery. (On my friends 2010 Hyundai Sonata I got regular readings.) I obviously was doing something wrong, but I did not know what it was.
Time to call in the experts. I have made somewhat friends with my local mechanic. (Always a smart move! The guy really knows his stuff and is a real nice guy.) I brought it in for diagnostics. Comes back and tells me that the TPS is bad. Sounds like he read it and graphed the voltage. Says I bought a defective part. (This time I think I finally took too much advantage of him. Unlike in the past he charged me for diagnostics.)Time to bring the TPS back to advanced and exchange it.
Replaced TPS and erased codes. Same problem.
What's up over here? I am thinking must be a wiring problem with the TPS as otherwise he would not have gotten messed up voltage readings for the TPS. That is bad because I clearly do not know what I am doing with electrical wiring (I could not even get a reading with a multi-meter) and I guess this is going to cost me a pretty penny.
Am I right about this? Is this a wiring issue? Can I really do what is necessary myself?
Thanks in advance for all your help!