Check for vacuum leaks, I was recording 19 liters per 100 kilometers
(97 870 GLT 2.4 turbo) which I calculate to be about 12.36 miles
per US gallon.

Two days ago I found a 1/4 inch vacuum hose that was disconnected,(drivers side
under the big tube that goes from the air filter to the turbo. Took the throttle body off and cleaned it, with a spray can of TB cleaner. Also took of the
idle air valve and gave that a good cleaning. Both had a lot of oil
in them perhaps due to my efforts to clear the inter cooler see below.

Have not had a refill yet, but the gas gauge has hardly moved for about 50K.
So there seems to be an improvement since re-attaching. Also the engine seems
more responsive.

But prior to that,on a very cold day,I had the intercooler freeze up. I could tell it was blocked as the big air hose from the inter cooler to the air filter was sucked almost flat when the throttle was opened. Of course the car had no power, and would not run faster than idle speed, until the inter cooler warmed up.

On three different days I dumped a container of gas line antifreeze (Methal Hydrate?) into the inter cooler to attempt to get rid of any accumulated crud.
Had to unclampe and pull the top hose from the intercooler.
The car really smoked each time after that. Finally it warmed up a little
and I got under the car to see if there was a drain plug on the inter cooler
similar to my 740 turbo. After removing the plastic splash shield I could not
see a drain plug. Removed the bottom hose from the inter cooler, and dumped another can of gas line anitfreeze, it just ran through. Put everthing back, stored the old black antifreeze for re-cycling, and sprayed TB cleaner around the TB but did not remove and do a thorough cleaning.