VSS importance

[Ludis Langens]

Here is a list of things affected by the VSS sensor.  This list covers
three different engines, two of them 4 cylinder TBIs.  All three
applications are from the same era as the 1226867 2.0 TBI.

Code 24
TCC lockup (auto)
Upshift light (manual)
IAC position learning (above 30 MPH)
Cooling fan control (not used in these applications)
Determine if manual transmission is in gear (compare VSS vs RPM)
Disable some idle speed control if manual in gear (see previous item)
Disable idle learn if moving
Enable idle learn if moving with manual in neutral
Prevent DecelFuelCutOff if manual in neutral
Prevent DecelFuelCutOff at very slow speeds
Top speed limiter (not used in these applications)

The third application adds one more item:

Amount to open IAC and rate at which to close it upon throttle closing

Note - the idle speed control logic is a rats nest of complicated code. 
It is hard to figure what really happens.

-- 
Ludis Langens                               ludis (at) cruzers (dot) com
Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/