i own a 2001 hyundai santa fe 2.4 liter i have had to change the throttle position sensor crankshaft position sensor timing belt and speed sensor other codes come up with oxygen and mass air flow sensor but i have not changed them yet i have been testing the fuel econ. and the first time i got 15 miles to the gallon the second time 18 the third 24 the forth trip 26 and last the fifth time 15 miles to the gallon which are all way to low what do i do?

 

If you have codes for the oxygen sensor and the MAF, then the logical thing is to replace them. Your MPG should improve.

 

yeah the car has 4 oxygen sensors is there a way to know which one is bad?

 

Well, yeah. What specific codes are you reading?

 

i will post all codes listed tomorrow, thanks

 

ok the codes are p0171, bank 1system too lean and p1701, tps open circuit which i already replaced but the code still comes up also alot of hesitation when driving i think thats because of this code and last p0101, mass air flow sensor

 

Try to clean your MAF sensor with a high quality electrical cleaner, don't use carb cleaner, or anything else harsh. MAF sensors are delicate and easy to mess up. A new one is $200 to $300. Note that codes do not clear themselves, they have to be erased by the scanner.

From odb-codes.com:

P0171

Basically this means that an oxygen sensor
in bank 1 detected a lean condition (too much oxygen in the exhaust). On V6/V8/V10 engines, Bank 1 is the side of the engine that has cylinder #1.

Note: This DTC is very similar to P0174, and in fact your vehicle may show both codes at the same time.

A code P0171 may mean that one or more of the following has happened:

* The MAF (Mass Air Flow) Sensor is dirty or faulty. Note: The use of "oiled" air filters may cause the MAF to become dirty if the filter is over-oiled. There is also an issue with some vehicles where the MAF sensors leak the silicone potting material used to protect the circuitry.
* There could be a vacuum leak
downstream of the MAF sensor.

Possible Solutions

Possible solutions include:

* In the vast majority of cases, simply cleaning the MAF sensor does the trick. Consult your service manual for it's location if you need help. I find it's best to take it off and spray it with electronics cleaner or brake cleaner. Make sure you are careful not to damage the MAF sensor, and make sure it's dry before reinstalling
* Inspect all vacuum and PCV hoses, replace if necessary
* Check for a dirty fuel filter and proper fuel pressure