[V8] cold weather killing gas mileage (AHA!!!)

[quickaudi at aol.com]

Guys, it never ceases to amaze me how many good uses a VAG-COM (or even better, an actual VAG computer that your new buddy who works at a Volkswagen dealership uses to run codes on your car) actually has.  We pulled the codes, and the only one that came up was 00537 - Oxygen sensor control - Adaptation limit exceeded.  Well, they obviously don't have the number reference for a 1990 Audi V8q at a Volkswagen dealership, so we ran the search for a car with similar programming.  00537 came up as Heated Oxygen Sensor (HO2S) heater circuit malfunctioning.  It is telling me to check the voltage from the relay and to check the wiring from the relay to the heater wires.  
This explains so much.  Basically, if we understand this code right, the oxygen sensor heater wires aren't getting either any voltage or full voltage.  When we restarted, we saw that it said intermittent, which really leads me to believe that I have a relay that isn't working quite right, as opposed to a bad wire, but I won't rule out either.  This is why my gas mileage was worse in the winter and better in the summer.  The heat from the day would actually help warm up the O2 sensor and therefore help it to read properly.  I've been running the car rich for quite a while, which kinda gets me.  I remember hooking the computer up to it a couple of years ago, and we saw the code, thought it was the 02 sensor, and erased it.  I later replaced the sensor, thinking it to be fixed.  This goes to show: run your codes!  At any rate, if anyone has any ideas about which relay to check, what to look for, etc., please let me know.  Maybe this will help some others on the list as well.
 
 
Joel
'90 V8q
'86 5kcstq