1993 Prelude fuel economy problems
 

I started having this problem quite a while ago. Now, since it got cold
outside it became even worse. I am getting at least 30% drop in my MPG.
On average I got about 24 MPG during normal highway and city driving.
Now i get about 17 MPG.
Recently I did full maintance on it. I have changed timing belt, spark
plugs, wires etc. I have not noticed any changes in the fuel economy
before and after my car got repaired.
My check engine light is off. In the morning car starts normally.

What should I check? Please advise.
Thanks

1993 Prelude 4WS
2.3L engine
175K miles
manual