Codes P2127, P2138, P0335 and P0452?

I bought it from the auction. Drove it off the lot and it felt like limp mode. I pulled over to have it towed. When I got it home. I found the shifter linkage was broken as well. It sat about a week as I waited for the linkage to be shipped. I installed the linkage, started it right up and drove it around a few blocks. The gas hand wasn't working. So, I drove it to AutoZone and bought a fuel pump. It started right up again, and I drove home. I installed the pump. The gas hand began working. But it would not start. I called a mobile mechanic who's very good at throwing parts on cars. But I don't think he owns a quality scanner that could give him more accurate diagnostics. We installed a new accelerator and crankshaft. Wouldn't start. He had me order a speed sensor. He said because the rpms weren't moving when it was turning over. Installed the speed sensor. Wouldn't start. He told me it needed plugs. I couldn't imagine that'd be the reason why it would be throwing throttle and crank codes behind a tune up. So, I towed it to the Nissan dealer. They looked at it really quickly and said it needs a new ECU. I couldn't believe that either. So, I towed it home and threw some plugs in it. Amazingly the car started right up and cleared all of the codes. I put a few miles on it. Drove it across town to the muffler shop to have an O-rings replaced. Drove it home. Sitting outside messing with the radio. The check engine light pops back on. Throwing all of the same codes. It's in limp mode again, very hesitant to start at all.