89 200TQ vs 90 200TQ

[scott.john.mockry@bangate1.TEK.COM]

Jim,

I have a 89 200TQ with the dual knock sensor MC engine.
Here is what I know about the differences in the 
89-90 200TQ's

When looking for a used Audi, check the build date that
is on the drivers door pillar. I have seen several 89
model 200TQ's with an early build date of 6/88. It seems that
Audi often makes changes to the new models in stages
and the later build date cars within one model year 
have the latest changes/improvements?.

The early 89 model 200TQ's have the updated interior
but may not have a drivers side air bag. Up until
VIN # K038261 the 89 200TQ's use the earlier (1986-88 5000TQ) MC style
turbo engine with the 7:8 to 1 compression, larger K26 turbo,
MAC11 Engine Control Unit (ECU), Single knock sensor etc.
Many people favor this version of the 10V MC Audi 5cyl engine
 when doing extensive  turbo mods (PDQSHP RS2 turbos, 
>250HP etc) due to the lower compression ratio which allows
more  boost.

The 89 model 200TQ's starting with  VIN number K038262 have
a different MC turbo engine with higher compression 8:4 to 1,
smaller K24 turbo (used on 91 200's and S4's?) for quicker
response at lower engine speeds, new camshaft with revised
valve timing and less overlap, dual knock sensors and more 
sophisticated ignition timing control MAC14 ECU. (allows
selected cylinder knock regulation. i.e. timing adjustments),
new intercooler with improved air flow, slightly different
fuel system with higher operating pressures/injectors and
a different pressure regulator scheme. These engines
give better low end response (torque) and are better
at around town driving but give up some top end yank
i.e. pull. They reportedly don't do well above 270HP.
Others may want to comment on this.........

The 1989 200TQ's and early 1990 200TQ's can 
have problems with the wood dash/door panel inserts 
clear coating clouding or fogging up which  doesn't look
very good. They supposedly improved this clear coating process
around 11/89 build date, but some have reported problems
even on the later cars.

I checked with a friend who is a local Audi mechanic and he indicated
that there were not too many changes on the 90 200TQ's. The drivers
seats have a lumbar adjustment and they went to a different type of
wood dash insert, avoided using some endangered species of wood
apparently. Others have reported that the 90 200TQ's may
have started using the coveted two piece exhaust manifold which holds
up better over time, less cracking, leaking etc. 
These 1990 model 200TQ's  probably had some additional unseen 
minor mechanical changes but I am not aware of any other major differences. 

Hope that helps
Scott M.