Tach stopped

I have a 88' Audi 90 non Quattro with 2.3 (NG) and 5speed. Last week the tach stopped working. Where does the tach get it's signal from. The wiring diagram I have says the "Speed sensor" but doesn't give a
hint as to where it is. Also I get a check engine light for about 3 mo that I can't seem to figure out. All sensors seem to be working. I average 33.1 MPG on Reg gas. O2 sensor voltage changes when I enrich or lean out the fuel mixture. Any help is appreciated as I want to fix this before the snow starts and things get worse.
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snipped-for-privacy@NotHome.yet wrote:

I don't remember for sure and I don't have the manuals anymore but it seems to me that the tach signal comes from the ECU. That was located in the passenger kick panel on the larger T4 series with that engine (had four of them).
To check the codes I would suggest going to AudiWorld and checking the history on the forum for your model. Some of the T44s had a place on the top of the fuel pump relay where you insert a fuse when the CEL is lighted to get the codes to flash on the CEL light. At that point you will need a code reference to find out what is wrong.
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Thanks, Tony, I'll checkout that website.
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Tony, Thanks you were right on. I went to AudiWorld.com and found the procedure for pulling the codes Via the Fuel Pump Relay "fuse trick". What I got were three codes I hope someone can ID for me. They are 2142, 2223 and 2232.
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Good to see you got the codes pulled. Not having the manuals any more I can't help with what they mean. If someone here doesn't have the information you might try to post the codes and ask for help on AudiWorld again.
Keep us advised of your progress.
snipped-for-privacy@NotHome.yet wrote:

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googled and here http://www.intendedacceleration.com/fault_codes.html
2142
Knock Sensor (KS) #1 (G 61)
Open or short circuit, Defective sensor
Check sensor and wiring
Symptom: Timing retarded, High fuel consumption, power loss, Boost pressure not attained
2223
Barometric Pressure Sensor ( F 96)
2232?
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