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Knock Sensor defective?


I don't know if you have the later 89 200TQ MC engine with the dual knock 
sensors but
either way a defective knock sensor can cause a hesitation and reduced
gas mileage. The computer goes to a reduced (retarded) timing  settting if 
it senses
that the knock sensor(s) are not working. My 89 200TQ with dual knock 
sensors had
similar symptoms and I did not even know one of my knock sensors was 
defective until 
I used a friends VAG1552 scan tool to pull the fault codes out of the 
computer. You
can also hook up an LED across the fault code connectors to activate and 
out the fault codes on the later Audis.  The 86-88 5000TQ's and early 89 
used the dashlight and the connections in the fuel pump relay to activate 
and blink out
the codes.

Apparently someone had taken out the dash light bulb (check engine) on my 
(this was done by some dealer mechanics). My sensor had an internal 
problem that would cause the knock signal output to be intermittent.
There is a service bulletin indicating that Audi upgraded the connections 
these knock sensors to have gold plating and part of the knock sensor 
procedure involves replacing the three connector pins in the engine 
wiring connector. On the later 89 200TQ's if one sensor goes bad the engine 
only retards the timing on those cylinders that are monitored by
the defective knock sensor.

Hope that helps
Scott M.