The problem could be the BOV. If it's not recirculated you're going to be going quite rich whenever you come off boost. Also, if the spring tension is too low it may be staying open at idle causing an excessive lean condition.
I don't recall ever seeing a code 31 in a MKIII Supra. Odd. Make sure the AFM connector is clean, dry and securely connected. Then reset the ECU and see if the code comes back. There's a list of codes in the FAQ section.
The KVAFM is an optical sensor. 99% of the cleaners people try to use either leave residue or fog the optics.
__________________
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 ---> 
|