High Fuel Consumption

I used to get 15-18 MPG city driving and 20-25 MPG free way driving in my 1990 BMW 735 IL.
Now I am getting only 13 MPG city driving and 15 MPG freeway driving.
Sometimes car runs smooth and other times there is a miss during idling and driving slow or fast.
I have installed new spark plugs and a fuel filter, but fuel consumption has't improved. Could someone help.
Regards
Bernard

Try a new 02 sensor, has that been replaced in the last 100k?
Usually a sign of a problem, ie: poor mpg & rough running....Ron

like the other guy said change your o2 sensor while you are it get a new throttle positioning switch, a k&n filter,new wires never hurt but you are looking ant about $400.00 in parts good news is you can do it yourself i did and full gas tank runs me about 1 1/2/ to 2 weeks depending on how much i drive o almost forgot very important change fuel filter its under gas tank aeasy to chane very important call me if need help riko 561-310-8800

ffff

get fault codes read out. with the o2 sensor it can help replacing it after 100,000km, but as the dme has adaptions, and the dme will adapt to the o2 sensor getting older. it would most likely be fine to still use.
dont go replacing parts if there is nothing wrong with it.
id highly reconmend doing a on car fule injection service to clean the infectors and carbon off the valves. then clear adaptions.
also the m60 motor which u have do get inlet manifold leaks and pcv leaks once they get some km's on them so check for leaks and check the vacume on the pcv system, just lift the oil cap when engine is running if its really hard to pull off because of, high vacume them u need to replace the pcv, which means intake manifold off.
i garentee this will reduce ur fule consumption