If the car idles alot, run some Seafoam thru it, it definitely made a difference with my '88 GT. The car had 39k miles on it but had sat so much and never been driven hard it was carboned up for sure.
Yea, Ive used Seafoam before, ill probably do it before the next oil change. It funny that the thermostat was mentioned, the temp gauge needle hardly gets up 1/4 of the gauge, even when its fully warmed up. I know these gauges are rarely accurate, guess ill hook up an external gauge and see where its really at.
There are so many factors in this. It's odd how sometimes a car will pass smog just fine yet not be running well at all. I have seen many times (working in an independent shop for 13years) cars come in with clogged exhaust and they pass the sniffer just fine yet drink gas. That equipment if running right can clean up a lot. Also if it's an auto, issues with the transmission can cause this. Torque converter not locking up or it skipping gears will do that. Once again, so many factors here. That isn't normal, foxes usually get decent MPG.
Let me add, that usually most EFI Fords from this era had rather white plugs, as they burn lean most of the time. Autos from this era also drank gas. I hate the auto in these cars. Mine has an auto, my TKO500 is not in it yet, two jobs no time. Anyways, damn POS goes straight into overdrive as soon as it can. I'm in my neighborhood at 25mph and it's in overdrive. Then I approach the hill and it waits until you have the pedal way down for a while then it downshifts. It made driving it suck when I had the 2.73 gears in it. Put in my other 8.8 with the 3.73's and it's not near as bad but I keep it in D when not going over 45, then put it in OD when I want to cruise. This helped. After getting used to the 4L65E in my truck, this AODE is a joke.