Improving fuel economy for the 1991 200q 20v

[Eric_R_Kissell at whirlpool.com]

Occasionally we have threads on this list asking about what fuel economy
people achieve with these 1991 200q 20v cars. The standard  answers are
usually 16-21 mpg around town and 25-30+ mpg highway.  I am curious about
possible causes for lower than expected mileage for the 1991 200q 20v cars.
Conversely, I am thinking about what changes could be made to improve fuel
economy. It seems many things are controlled by the ecu, but there are
still many things that could affect fuel economy.  I have read about enough
variation in results on this list to make me curious about whether everyone
could be getting 30+ mpg for highway driving. For the record, I see 16-21
around town (depends mostly on my right foot) and 25-28 highway.

Any ideas?

Some factors I can list, in no particular order:

tire type (snows, all season, touring, summer performance, etc)
tire/wheel diameter
tire/wheel width
tire/wheel weight
gasoline composition (alcohol content, etc.)
gasoline octane
chip programming (not all aftermarket chips are the same)
spark plug condition
spark plug wire condition
multi-function temp sensor condition
block temp sensor condition
coolant operating temperature
oil operating temperature
engine oil type
engine oil weight
engine oil amount
transmission oil type
transmission oil weight
transmission oil amount
cat converter flow
exhaust sytem flow
exhaust manifold (stock, RS2, header, etc.)
O2 sensor condition
terrain (flat, e.g. NW Ohio, or rolling or mountainous)
elevation
roof rack or no roof rack
suspension ride height
intercooler effectiveness
fuel pressures
turbo type
intake tract flow/restrictions
shift points
weight of driver's right foot

So, what can you add to the list?
What should be dropped?
Once we have a good list we can prioritize by ranking from most
likely/important to least likely/important.

I am thinking about doing some experimentation, but I want to identify the
best factors I can manipulate and/or test across. Yes, this is the type of
thing I do in my "spare" time.

TIA,
Eric Kissell
Tiffin, OH 44883
1991 200q 20v Avant, Koni Sports (yellow), 2.4 Bar (MRC), eBay Surprise
1989 200q 10v Avant, Boge Turbogas, 1.8 Bar (qlcc) - FOR SALE
1986 5000cstq Sedan, Bilsteins, 1.8 Bar (SJM)