89 90 ECU diagram

[Ben Swann]

Great job of gathering the info Huw.  I edited for clarity and put in order of pins.  

I did not verify the color or function, so be sure to double check when using this.  If
there are descrepancies, let Huw & myself know so we can make corrections.

Huw, I take it ICU means Idle Control Unit?

Ben
http://www.gtquattro.com

ECU Pinout Audi ‘89 90

There isn't a simple pinout diagram but info can be gleaned from  
"information" spread over roughly 30 pages of the Bentley manual.

Hold ECU connector cable with left hand. 
1 to 18 are the top row & 19 - 35 are the bottom row:

1 w/gr ICU
2 br/w bridged to ground on 1988 only?
3 bk/r NTC temp sensor
4 r/y and 5 r/w go to the Differential pressure regulator DPR 
7 gn OXS signal
8 br OXS shield (ground)
9 br/bl - t6b
10 y Instrument cluster on board computer
11 
12 
13 br/g ignition CU
14 bk/bl power s28 transmission related
15 y/r charcoal carbon canister solenoid
16 br cold start valve (CSV)
17 g/r Idle Stabilizer Valve(ISV)
18 br/r ground
19 bk/r power s19 
20 br/y goes to black 6 point connector rt side engine compartment
21 w/r ICU
22 br/bk same harness ("t6b")
23 gy/g potentiometer (air flow)
24 g/r 8 pin connector on right side engine harness "t8"
25 gy altitude sensor & ICU 
26 bl/y ICU potentiometer
28 bl/w idle switch in throttle switch
29 
30 w/bl ignition control unit 
31 bk/v WOT switch in throttle switch
32 bk/y [T8] 
33 bk/gy AC 
34 br ground transmission related
35 br/r ground AC-related