code 41: your TPS is either out of adjustment. it needs to be calibrated, or if it's fried, replaced.
here's how to check/calibrate it:
http://www.cygnusx1.net/supra/library/TSRM/fi/FI_101.html
code 43: starter signal. try checking all your grounds, first. take off the negative lead from the battery, then take the positive lead off the starter and clean it up super well.
(*disconnect the negative battery cable first, lest you short out the system when you take off the positive from the starter if you touch something metal!!!*)
check for any loose, bare wires, etc...
code 51: i've NEVER heard of it being the A/C thats causing the problem. most commonly, code 51 is the TPS, as well.
if it ends up that you cannot properly calibrate your TPS, call Jay Marks toyota (champion), they're a vendor on our forums here. jeff will hook you up with a new one for mad cheap.
-shaeff