[Supras] Failed AFM?

[Michael Green]

Recently a problem with the Supra occurred, which I would appreciate 
opinions from list members on.
At engine idle, air fuel ratio will become increasingly rich. Per the wide 
band, it will increase from 14.5 to 1 to over 9 to 1. Anything more than 9 
to 1 and my wideband will display "RICH".
Code 31 is persistent (AFM signal) and returns after pulling the EFI fuse. 
No other codes occur.
I have checked wiring from AFM to ECU, continuity is good. Voltage checks at 
ECU wiring terminals are within normal values, per TSRM, except the KS (air 
flow meter) voltage.
Per the TSRM, the voltage at KS with ignition switch on, should be between 4 
to 6 volts. I have 5.18 volts. However, with the engine running, the KS 
voltage should be 2 to 4 volts. My voltage remains at 5.18 volts. The 
voltage does not drop until the engine RPM reaches 2500, then it will bounce 
between 2 and 3 volts and the A/F ratio will drop to 14.5 to 1.
If I slowly reduce RPM from 2500 to idle, the A/F ratio will bounce back and 
forth between rich and lean. KS voltage is bouncing from around 3 volts to a 
bit over 5 during this RPM drop.
Resistance for the water temp sensor and injector cold start time switch are 
normal, per TSRM.
At this point, I decided to take a break and ask the list for help. Does 
this sound like an issue with the AFM?
Input requested. Thank you,

Mike Green

_________________________________________________________________
Play Flexicon: the crossword game that feeds your brain. PLAY now for FREE.  
  http://zone.msn.com/en/flexicon/default.htm?icid=flexicon_hmtagline