[Diy_efi] air flow meters

[dan at w3eax.umd.edu]

Hi Guys (and/or Gals),

This isn't quite DIY_EFI but I'm sure someone here must know the answer to 
my question.  I have an 85 MR2 (which I'm sure will eventually get some 
DIY EFI) but for now it has Nippondenso injection which is a licensed copy 
of Bosch L-Jetronic featuring the standard vane/volumetric airflow meter.

Besides the fuel pump control and the air intake temp thermistor, there 
are four pins: Vb, Vc, Vs, and E2 (ground).  The Toyota manual has a 
schematic that shows something along the lines of:

Vb -\/\/\/- Vc -\/\/\/-Vs-/\/\/\/- E2 (where Vs is a wiper of a pot)

Toyota claims the resistance between Vs and E2 will "fluctuate" between 
20 and 3000 ohms as the flap is openned.  Bentley's BMW service manual 
claimed the resistance should increase "steadily without any flat spots as 
the sensor flap is moved to the full open position."  Bosch's "Automotive 
Electric/Electronic Systems" claims that "The angular position of the 
sensor flap is transformed by a potentiometer into a voltage."

However...  Toyota also claims the resistance between Vc and E2 should be 
100-300 ohms, and the resistance between Vb and E2 should be 200-400 
ohms.  My resistance is 180 and 280 ohms respectively, I don't see how 
this jives with the 20-3000 ohms claimed earlier.  But it gets weirder.

I tried pushing the flap in and measuring the resistance between Vs and E2 
and it seems to start at about 120 ohms and then increases, but at about 
3-400 ohms it starts dropping again, then increasing, then dropping, etc. 
The most I've ever seen is about 900 ohms and often its only 600 ohms.

I opened the meter up, and the inside looked clean and in excellent 
condition.  The potentiometer was a dark material laminated onto a PCB 
which appeared to be "toothed."  It was almost as if there were a bunch of 
potentiometers in parallel with the wiper moving from one to the next. 
Its hard to describe.

Can anyone explain whats going on with this and what it SHOULD be doing? 
Is it right, is it wrong and fixable or do I need a different AFM?

dan