[V8] Re-birth of my '90 200 tq - Part Zwei

[Brian K. Ullrich]

Howdy from Texas, y'all. For those of you following from home, here's the
latest on my 1990 200tq 10v project:

When last we checked, the old girl had new unders, from stem to stern.
Running gear is in top order, but we had 2 minor driveability issues:

1. She idled rough, and failed a Tx state inspection by having a high
hydrocarbon issue at low RPM.

2. An engine buck induced at 1.7bar indicated on the boost gauge.

After consulting with my local club (http://northtexasaudigroup.com), I got
some assistance from a guy that knows CIS cars inside and out. Due to
schedule concerns, he gave me several items to check before he showed up.
All proved benign (check certain hoses, do a spray check for vacuum leaks,
etc).

And then...it happened. Holy Smokes...you'll never believe what the root
cause was.

First...some background (of course):

After the second Tx State Inspection failure, I was stumped. I conferred
with the inspector, and he advised me that in his opinion, the car was not
running rich. His analysis of the gas readouts indicated to him that the car
was actually running efficiently, but was not burning fuel well at low RPM.
This made him think it was in the ignition loop somewhere.

Of course, he's not an Audi guy, much less a CIS-III Audi guy, so I took it
with a grain of salt. WRONG.

In the course of troubleshooting every possible scenario while waiting for a
local expert to come to the rescue, I took the car to my brother-in-law, who
works at a local garage. He wanted to perform a gas analysis, the basis of
which could be used for Plan B: retard the ignition timing to a point where
the hydrocarbons were within acceptable limits for inspection, and then we
could put the timing back.

While he was hooking up the gas analyzer, I began reading section 28.32 of
the Bentley manual (Adjustment of timing), and in doing so, I found a
curious item. One of the procedures called for the "bridging" of the fuel
relay with a 5 amp fuse; simply insert the fuse with the car running, and
within 4 seconds the car would essentially revert to "base timing", upon
which accurate adjustment could be made.

Well, I'd seen that fuel relay. Many times. It had a 5 amp fuse inserted in
it, which I had myself checked it several times. It was yellow. It was good.
Could this...? Nah...no way. But what if...?

So, I pulled that fuse out of the fuel relay, and the car immediately idled
properly, and the hydrocarbons shown on the gas analyzer showed it to be
WELL within limits for the state inspection.

Well, hell, I beat feet straight back to the inspection station and, sure
enough, she passed. In fact, the analysis of this last inspection indicated
that she's running VERY efficiently.

So...wow. While the car had been at my local shop over the past year getting
little things done here and there, one of the mechanics and I had gotten
into the habit of pulling the fuel and power relays each time so the car
wouldn't be able to be started, therefore not stolen. And that damn fuel
relay had that "bridge" fuse in it the entire time. I'd been putting it back
in the car just like that for nearly a year. I never thought to check it as
a cause for the idle/inspection issue.

The fuse essentially disables the fuel advance, so any timing activities
would provide a more accurate reading. But with it in the car, it threw the
whole fuel/air/spark mixture off enough at low RPM that it wouldn't pass
inspection, much less idle correctly.

Sometimes, it IS the little things.

Next...address the turbo buck. And the cruise. And the radio. Then the
driver's side door switches. And headliner. Then drive it for another 200K.

As we Texas Aggies say...WHOOP!