[Supras] Failed AFM?

[Walker, Brian1 (Rich. Dist)]

Mike, are you by chance using an oil type air filter? (K&N or similar) I've had similar problems that appeared to be cause by buildup on the AFM sensor over time. I have also heard others mention the same problem. Historically there has not been a method (AFAIK) to clean the very sensitive mirror in the AFM sensor. I have seen a MAF cleaner advertised in some magazines that may work (CRC Is the manufacturer,   <http://www.crcindustries.com/auto/content/products.aspx> http://www.crcindustries.com/auto/content/products.aspx) but I have not seen this in the store to try it. We had tried different agents that we 'thought' would leave no residue but still the sensor failed and triggered code 31.

Hope this helps, 
Brian W-88T 

Date: Sun, 18 Feb 2007 12:41:35 -0800 
From: "Michael Green" <> 
Subject: [Supras] 
To: supras at supras.com 
Message-ID: <BAY123-F20E4172B41C75FDC14C747CC8B0 at phx.gbl> 
Content-Type: text/plain; format=flowed 

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