About a month ago I used Mopar Combustion Cleaner to improve my mileage, which it did by a significant ammount but when spraying the cleaner into the throttle body the CEL came on, turns out it was for the A/C system which as not worked in a long time. So I reset the PCM, removed neg. batt. cable and let it sit over night. Car stumbled and died like it should then started up normally. Now my mileage has gone from 250-260 per tank to 200 per tank. When the engine is first started and its very cold out the exhaust reeks of gas, its obviously running rich but it runs perfect, no misfire or anything, no codes. Nothing obvious is out of the ordinary.

If the O2 sensors were not working correctly would it throw a CEL or code?

The car is a 96 SOHC

 

maybe give it a while to reset itself?

 

I can't be exact on how long, but the PCM should be set-up after a short time of driving. Your milage is very much dependant on how you use your right foot, the temperature outside (a car in 30 degree temps takes longer to get to operating temp), hills and declines that you drive. I really don't think that useing a Mopar cleaner would make that much of a negative differerance. Try bench cleaning the TB.