Volvo: Volvo 1988 740 GLE SW Running Rich(12mpg in city, 20 High Way) (141K)., air flow sensor, fuel pressure regulator

Question
This car was garaged due to a no start for a while and then we started working on it and we got it running after replacing the Power stage at the left fender also we changed the Air Mass Meter. The problem with the car is that it runs very rich. We changed the Fuel Pressure regulator but still run a little rich. What are the other remaining possibilites that we need to look at?
I think there is the O2 sensor but it is so expensive around $90. Also, from my reading there is something called the Engine Temperature sensor which might make it run rich since the computer sees signals that say the car is cold and needs more fuel. Do you have any other ideas? Also, does these two things seem to be the way to go about to adjust the mileage per gallon for this car?

Thanks very much.


Answer
I think you're going in the right direction with the O2 sensor and engine temp sensor, both of those will cause the computer to adjust mixure and time.  Another thing that comes to mind is simply a gunked up throttle body, especially if the car has been sitting for some time.  A partially clogged air intake (further back behind the air flow sensor) can cause the computer to make adjustments as well, albiet to a leaner mixture in that case.  But because clogged throttle bodies are so common in these cars, and because it can be the creator of many problems, I would look into giving that a thorough cleaning.  Good luck!