My '92 LeBaron has both instant and average in the "Traveler" trip computer. Most Mopar (Chrysler, Dodge, Plymouth) cars from that era had this feature available.
Average mpg always has read below calculated mpg at the pump though. The "distance to empty" feature is also always reading less than I think it should. *shrugs* I'll take conservative over optimistic though.
I can verify that the late 80's early 90's saab 9000 have an instant and average economy meter. It might have been an option on the 900s. The 900's all had a painted on green/yellow/red on the tach for economy. I think the green was below 2200 or so.
Its depressing to watch the instant fe meter in a 99 jeep grand cherokee, but i'm still glad they put it in there.
Only those with the MFA (multi-funktion-anzie something) known in English as the multi function display, mostly the GLX top-of-the-line trim models which include the VR6 engine. '95~97 Passat GLX, '95~99.5 Jetta GLX, 95~99 Golf GLX. Many of the later ('98+) VW also have this feature as part of an upgrade trim level option.
The accuracy in these is dependent on the injectors. Stock injectors produce a display number lower than actual, high flow performance injectors produce a very optimistic display number. The computer can be offset to more closely produce numbers in line with actual, but until I have some more data to determine the correct offset, I'm using the dash display as a better / worse reference and the re-fueling pump display and odometer as the actual fuel economy.
Chrysler Town & Country Minivans, 1994 and 1998 both have it. They have both an average number and a real time number, which is updated about every 2-5 seconds, but on some kind of a running average basis.