Poor Saab 9-5 2003 Vector mileage fuel economy?

[saab_9_3]

There are a lot of reasons that can cause poor gas mileage (yours sounds particularly bad):

1) Has the car been tuned up recently? That can negatively impact gas mileage drastcially? A bad air filter can really hurt gas mileage (and a lack of a tuneup would cause that).
2) Are all the vacuum hoses connected and not leaking? You will burn extra gas if there is no vacuum. Usually you will have a rough engine with stalling if this is the case.
3) Checking the O2 (oxygen) sensor for a malfunction. This can cause poor gas mileage.
4) A part called the OEM PFR could be malfunctioning. Not as likely as the first two but a possibility.
5) Check for wet spots on the gas tank by looking under the car. This is very unlikely but still a possbility if the tank is having issues.
6) Again unlikely, but leaking fuel injectors could cause this.
7) Again, unlikely, but a blockage in the exhaust system can cause gas mileage issues.

This is a lanudry list, some more likely than others. This is like looking for a needle in a haystack but very rewarding when you find the issue.

 

[MongBalls]

I've got a Saab 9-5 2003 Vector, standard 2.3T engine.
Bought it about 3 months ago, drives well most of the time.
Issues are, poor fuel mileage. averaging about 13-15 litres/100km and when it gets to a really hot day eg last week 40c the mileage goes up to 20L/100km!!
On the really hot weekend when i went to park the car, the car stalled twice, and sometimes the power dips down and comes back up when its stationary.

What do you think it could be?
I've changed the plugs last month (had a saab tech do this)
The pullys and serpentine belt were changed.
Could it be a vacuum leak somewhere?? What else could be the problem?

Most people brag about great fuel economy of these things but i've got the opposite, even the big toyota 6cyl 3l engines have great fuel eco of 10l/100km
for you yanks out there.
15L/100km = 15.6MPG
20L/100KM = 11.7MPG