Volvo Repair: Volvo 1988 740 GLE very low city driving gas mileage., coolant temperature sensor, volvo 740 gle

Question
I have a B230F engine 1988 Volvo 740 GLE non-Turbo that is making with AC running 50% of the time 23-24 mpg on the highway at 70-80 mph. Without AC, 24-25 mpg around same speeds. The car has 155000 miles on it. Whereas in city driving i.e. stop and go traffic, the car does really really horrible something like 15-17 mpg at best. I have changed Air Filter, Fuel filter, plugs, wires, fuel pressure regulator. Used many bottles of fuel system cleaners etc. I was told through a google newsgroup that I might want to change the Engine Temperature Sensor. I searched at parts sites and local Autozone and AdvanceAutoParts and they got me a part named Coolant temperature sensor as the one I am looking for.

My question now is:
1# Where exactly is the temperature sensor located? If I need to change it, does it suffice to get a used one from a junkyard or it better be new?

2# Do you have any advice for the strange low city  mileage?

3# At the dealer, they do throttle body cleaning. Is this something I should do?

4# What would be a reasonable mileage for such a car?

Answer
Hameed, sorry to tell you but that is about right for gas milage on these engines.  They are not very fuel effiecient.  The Ect sensor is under the intake manifold but you would know if that was bad because the car would run terrible or wouldnt start at all.  The coolant temp sensor is the alternative name.  Better to get one new.  You are getting about the milage that car got when it was new.  Throtle cleaning should be done every 30K miles. Roger