Mercedes Benz repair: poor gas mileage, poor gas mileage, new distributor cap

Question
Hi Josh:
    I own a 89 mbz 300e with 142000 miles. I'm the second owner. Most recently, the car has poor gas mileage  14-15mpg combine mostly highway.  I had the spark plug and wires changed, fuel filter, air filter new distributor cap and rotor. No check engine light.  Car runs well but only problem is poor gas mileage.  Can you help? (passed smog OK)
Thanks in advance!
Stan

Answer
There are a few things that can cause poor fuel mileage. One thing that is most commonly overlooked is proper tire pressure. If your tires are low on air pressure, that can greatly reduce gas mileage. Another problem can be leaking fuel injectors (you would have to have a technician check that). The last common problem is the o2 sensors (once again, you should have a technician test those for proper function).