When he throttle is closed... guess what... it's supposed to be CLOSED. Quit dicking with things you have no idea about just because you think it might be a good idea and go buy a service manual. The idle is controlled via a computed controlled valve which bypasses the throttle body altogether. Your code 51 indicates a possible problem with the switch that's built into the TPS to tell the ECU when the throttle is closed.
Look in the MKIII FAQ section for a thread on diagnostic codes for a list and descriptions of the various codes.
__________________
If something breaks or you need to contact a member of the administration please post HERE. Unless it's a private or administration matter please post it on the forum. It benefits no one else if car related questions aren't posted for future users and takes away from the time I'm able to spend helping on the rest of the forum.
If you're so inclined I'm always more than happy to accept tips via PayPal. 
Tip Jar ---> 
|