Ur-q Idle Switch

[Dave Lawson <dlawson@ball.com>]

Andrew/Phil,

>
> What function does the idle switch have on an 81 TQC w/o oxygen sensor
> or frequency valve. When I open the circuit and the engine is at idle,
> the engine speed increases. What causes this? What is the computer
doing? 

All good questions.  It's hard to see what it _can_ be doing, looking at
the 
diagrams.  It looks like the ECU in a 1981 car only has two outputs -
ignition 
timing and power to the fuel pump relay.  I would guess that it must be 
changing the ignition timing, and I'd suggest you check the timing marks

against one another.
>
The ur-q uses the idle switch to determine when the throttle is
open(when the
idle switch is open) and when the throttle plate is closed. It needs to
know 
what the throtle plate is doing in order to determine ignition timing.
Above 1000 
rpm with open idle switch, the ignition timing is based off the timing
map. If the 
idle switch is close and engine speed is above 1000 rpm, the ECU follows
a 
deceleration timing curve. When the idle switch is close and engine
speed is
below 1000 rpms, the ECU performs its idle stabilization function. The
ignition
timing in this region is as follows

<600  rpm           engine cranking speed, idle stabilization not used
600-720 rpm       ignition timing set to 26 deg BTDC
720-820 rpm       sloped from 26 deg BTDC to 6 deg BTDC over the 100 rpm
region
820-1000 rpm     idle stabilization not used, timing set to 6 deg BTDC

This information (and much more) is covered in the quattro introductory
service training
information booklet.

HTH.
-
Dave Lawson
86 gt
83 ur-q