O2 Sensor help

[ghatch]

I have a 2012 Golf Base Automatic with the 2.5 motor. I seem to be getting pretty lousy gas mileage. Around 19 in the city. I've changed the plugs, coil packs and air filter with no improvement in MPG. OBDEleven detected a dirty throttle body so I cleaned that. Maybe has more power but did not help with MPG. It runs fine and the idle seems pretty smooth. I'm thinking maybe try the upstream O2 sensor? Anyone ever change that and see a boost in MPG? It isn't throwing any codes but I assume it could still not be performing well. Car has 115k. I bought it used. I see no evidence that the O2 sensor has ever been changed in the service history. Suggestions?

Thanks!

 

[GolNat]

You can try cleaning the sensor instead of replacing it.

How are the tires? What pressure you running? What is the expected MPG? If you are 2-3 less then average its most likely driving habits.

 

[ghatch]

the tires are pretty new. I set the pressure to what is on the door jamb. 32 or 36 or whatever it says. Its supposed to get 24 city and I'm getting 19. Its my teenage daughter driving it. She may have sort of a heavy foot starting from a stop, but I don't know if that explains it all. She almost never goes on the highway so it is true stop and go city driving. I'm pretty sure something isn't right. The O2 sensor isn't all that expensive, I just need to buy the special socket and it looks sort of hard to reach behind the engine.

 

[MLue1]

Sounds like you're on the right track, hard to read things when the car seemly runs well.

Since you cleaned the throttle body you can re-adapt it as well, ... can't hurt!

As well, if you have a MAP sensor that's on its way out that can also affect your milage coz it not only reads the air pressure but the temp of the incoming air as well.

Keep us posted.

 

[Wascally Wabbit1]

Ya, 18 mpg is not right, even with a heavy foot. I did have a situation with my last golf where the mileage had gone down (but not that low) suddenly but I did have a code when I checked and it was an O2 sensor. I replaced them both (California models have 3, 2 downstream) and the mileage did go back to normal. I usually get mid-20's around town, and low 30's on the hwy, and high 20's combined. The car is tuned though so that added a couple mpgs.

 

[ghatch]

I should have swapped the map sensor when i did the throttle body cleaning. I think its right below it. I did re-adapt the throttle body. I hate throwing money away on gas! I guess those are potential things to try. O2 sensor and map sensor. replacing an O2 sensor with 115k doesn't seem like a bad idea no matter what. Isn't the upstream the most relevant to fuel economy? I don't know how many that car has. 1 or 2 downstream I guess.

 

[MLue1]

Since there are no codes for the efficiency on the CAT we can asume the downstream O2 sensor is working. However if the CAT is partially blocked/clogged it can affect fuel milage, BUT I've never heard of a clogged CAT on any VW.

 

[Wascally Wabbit1]

I should have swapped the map sensor when i did the throttle body cleaning. I think its right below it. I did re-adapt the throttle body. I hate throwing money away on gas! I guess those are potential things to try. O2 sensor and map sensor. replacing an O2 sensor with 115k doesn't seem like a bad idea no matter what. Isn't the upstream the most relevant to fuel economy? I don't know how many that car has. 1 or 2 downstream I guess.

Yes, the upstream 02 sensor is for the air/fuel. In my case I only had a code on one of the downstream 02 sensors, but with the sudden gas mileage change I replaced them all as the car had over 100k miles at the time. I was refering to the downstream sensors in my prior post (when I said I replaced both) due to the code but I actually replaced the upstream as well.