Fault code 2233 ?! ('87 5000S Q)

Hi all,
I'm stumped what to try next. On my '87 5000S Quattro I'm getting Fault Code 2233 - Air Flow Sensor Reference voltage, or from Bentley's:
Code:    Location:
2233    "Reference (supply) voltage for air sensor potentiometer and altitude sensor"
Problem: "No reference voltage from Terminal 21 or ignition control unit to Terminal 26 of fuel injection control unit"
Repair: "Check wiring between electronic ignition and fuel injection control unit using wiring diagram"
I've checked this wire, as well as wires between ECU (injection control unit) and all related devices, such as air flow potentiometer, temp sensor, cold start valve, idle stablization valve; and test each device except the air flow potentiometer. I've also replaced the ECU (injection, not ignition).
Before I replace the ignition ECU and start a massive wiring check, can anybody steer me to a area that they think might be the root cause? Oh, the behavior is that it idles high, random ignition cut-out, and the cold start valve wasn't working (tho cold-start may now be working -- it started okay just now, tho before it had been requiring 30-60 sec of cranking before starting - hot or cold).
TIA, Jaz
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Sorry, no BTDT on this one.
Just a thought. Sometimes when there seem to be multiple symptoms the cause ends up being a bad ground. Also, I didn't think that the '87 Q NAs had a separate ICU (in the drivers kick panel on my '91 100Q). If it does have this, some people have found that rain / water has migrated somehow into the plastic bag that the ICU is enclosed in and has corroded the multi pin connector. Cleaning often corrects the problems.
Seems that I heard that the ICU optimizes engine management but in the absence of information from the ICU the ECU operates things in default mode. This might be a SWAG.
You have really done your homework on this one.
Tony '91 100Q 5spd
Jaz wrote:

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Yes, this one has both ignition and injection ECU's (must be CIS-III), and today I tried swappig out the ignition ICU, but that had no effect... still the 2233 fualt code. And each ECU is clean with no contamination or corrosion. Tomorrow I'll check resistance ranges on the air flow potentiometer. OTOH, I must say that aside from the high idle, the runs well once it starts.

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I'm an idiot.
But Tom Chudzinski is not (sorry to post your name here, Tom, but you deserve recognition for this)
Tom wrote to me and said: "Are the fuses in positions 23 through 28 good? (perpendicular to the main fuses in the main fuse box) Often the schedule in the fuse box will say "unused" or "open" but . . . . . sometimes they are needed. Some Audis use position 24 to power the CIS-EIII controls, some use fuse 28. THEY MAY NOT BE "EXTRA" FUSES!!!!! Many useless diagnostic dollars have been spent and many a bald man has been created over this issue. Often the published repair manuals are incorrect in this area."
Sure enough, and I'm embarrassed to admit, I neglected to stuff a fuse in position 28 despite that it obviously had contacts in the socket, whereas the other 'spare' sockets had none (not to mention that long ago I replaced my cracked fuse panel cover with one from a junk yard, but when I dug out my original cover it clearly lists #28 as 'Engine Timing'.) Sometime over the past months I must have used #28 as a spare for another blown fuse, and just didn't but two and two together.
Oof! Oof! Oof! (that's the sound of me kicking myself).
Thank you all for your help, Especially Tom who reminded me of the DFC's and ultimately the fuse solution.
Humbly, Jaz

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Eureka! Glad you got it running, Jaz. As I recall I think I did the same thing on time when I was working on mine. Pulled out a "spare" fuse, and then the engine didn't work right. I forgot how I finally identified the problem, but it was a bugger.
Congrats...
--
Stephen Clark
89 Audi 100
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Good to hear you have it figured out and cheaply at that.
I guess I did have a BTDT. Had the same experience and should have thought of that.
slapping self in forehead.
Tony '91 100Q 5spd
Stephen Clark wrote:

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I'm an idiot.
But Tom Chudzinski is not (sorry to post your name here, Tom, but you deserve recognition for this)
Tom wrote to me and said: "Are the fuses in positions 23 through 28 good? (perpendicular to the main fuses in the main fuse box) Often the schedule in the fuse box will say "unused" or "open" but . . . . . sometimes they are needed. Some Audis use position 24 to power the CIS-EIII controls, some use fuse 28. THEY MAY NOT BE "EXTRA" FUSES!!!!! Many useless diagnostic dollars have been spent and many a bald man has been created over this issue. Often the published repair manuals are incorrect in this area."
Sure enough, and I'm embarrassed to admit, I neglected to stuff a fuse in position 28 despite that it obviously had contacts in the socket, whereas the other 'spare' sockets had none (not to mention that long ago I replaced my cracked fuse panel cover with one from a junk yard, but when I dug out my original cover it clearly lists #28 as 'Engine Timing'.) Sometime over the past months I must have used #28 as a spare for another blown fuse, and just didn't but two and two together.
Oof! Oof! Oof! (that's the sound of me kicking myself).
Thank you all for your help, Especially Tom who reminded me of the DFC's and ultimately the fuse solution.
Humbly, Jaz

{ Please excuse the 'burp' when replying }
forgot to take the pills and typed:

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