Hi im getting codes PO107/Po138 and Po139 on s40 volvo 2002 2.0t sport petrol is it best to change the map sensor first and see if that clears the other problems .

Located under the front of the cars engine frame just below the radiator

Just because your getting a code from a sensor doesn't mean the sensor is N/G. The MAP sensor reads the manifold air pressure, that can be anything from a vacuum leak, elec short, bad plug/wire, miss, gasket and the list goes on. It can be a bad sensor too, don't get me wrong. Does it run rough, hard start, did you ck the emissions? First things first Vacuum leaks & gaskets are popular. Once in a while I cross paths w/ a cracked manifold. Don't throw your $ out the window, Do it once & do it right. Good luck

The P0107 code is a bad MAP sensor circuit. Unless you replace the sensor, you can clear the code a million times, and it will come right back. And without that sensor, the engine will run rough, since the PCM has no idea how dense the air is to make adjustments to the fuel/air mix.

P0138 O2 Sensor Circuit High Voltage (Bank 1 Sensor 2)
P0139 O2 Sensor Circuit Slow Response (Bank 1 Sensor 2)
P0325 Knock Sensor 1 Circuit (Bank 1 or Single Sensor) -Circuit Malfunction
think you just need a new o2 sensor

do you have two o2 sensors after catalytic con.could be not good.

Unless is was the one doing the testing I can not say that it will fix the problem. I would check the fuel pressure, the fact you have a rich code (P0172) means you may have excessive fuel pressure and the sensor is reading that.I assume this is a four or six cylinder and you have only one bank of cylinders. Check the fuel pressure before you do any parts replacing.

P 107 is not MAF - (Mass air flow sensor), that code comes up as MAP (manifold absolute pressure ) sensor. ?

Try unplugging and plugging the map sensor, this device should have manifold pressure hooked up to it, via hose, so check for cracks or leaks. Then clear codes and test again.

code p 0138 refers to 2 items
1--heated oxygen sensor(HO2S) 2 bank 1--high voltage ==causes --wiring short to positive --HO2S---ECM
2--oxygen sensor (O2S) 2 bank 1--high voltage ===causes wiring short to positive ---ECM
code p 0139 refers to 2 items
1--- heated oxygen sensor (HO2S) 2 bank 1--slow response ===causes --heating inoperative --wiring--ECM
2--oxygen sensor (o2S) 2 bank 1 slow response ===causes --wiring --- O2S

heated oxygen sensors9HO2S) are in the exhaust manifold before the cat converter
Oxygen sensors (O2S) are after the cat converter
it is indicated that the HO2S is faulty-
check the wiring and /or replace both sensors

there is two sensors that those code refer too. The map sensor, and the iat sensor. and both would have an effect on gas mileage. Both sensors would just make the car run a rich mixture.