1992 Honda Accord Fuel consumption

It seems that after the last timing belt change the fuel consumption suddenly ecxeeded approx. 1 litre more. Timing is OK, Check engine lamp doesnt light. Sensors are OK, as for their resistance (IAC, TDC, CYL, CRANK ANGLE, IAT, ignition control unit, injectors). Ignition timing is checked, it's 15 degrees precisely. Idle speed is adjusted as it's described in the manual, it's 750rpm. I've changed the air filter, fuel filter, spark plugs. There is a momentary rough running after cold start, and some vibration on idle sometimes. Vacuum gauges are intact.