Instantaneous fuel consumption & STC problem

[Marihuana]

Hey Guys,
First of all, I thank you all. I have learned so much about my car. In my country, not many people drive Volvo and forums here not good. We are not used to DIY so people only share pictures of their Volvos, upgrades etc... Useless.

2 years ago I bought my 2002 S80 2.0T (gasoline) automatic transmission. It was not in a good condition, and I had to spend some money to make it look and run nice. Thanks to UK and USA forums, I did many fixes myself first time in my life. I am still learning. Wish I had my own garage to work on my car.

Anyway, here are the issues I am facing recently, and hope to get your ideas, offers, solutions.
When the engine is cold, instantaneous fuel consumption goes up to 99.9 lt/100 km. When engine is warmer, it goes up to 60s 70s when I am running. Trust I am not accelerating aggressively. Pls check below YouTube link for the short video

Other issue is the STC button light. It is generally no light on the button. Sometimes it is on when I start the car, but generally off. When it is off, Stc is functioning, ABS is functioning. Few days ago I removed each button and the background light is ok, but the small led on button not functioning. While STC button light not functioning, the other 2 buttons do work properly.

Any idea what consumption is so high and how to fix Stc issue?

Many thanks in advance.

[oragex]

When the engine is cold, instantaneous fuel consumption goes up to 99.9 lt/100 km.

I had this exact thing, front O2 sensor. Very high fuel consumption on bumper to bumper traffic. Not sure how easy to access is on turbo, I used two wrenches to lever and pry it loose. Ntk/Ngk works well, off Ebay, numbers are confusing

[Marihuana]

Hi Oragex. Now I am almost sure it is O2 sensor. I had some research after opening the topic, and yes all were O2 sensor issue. One of the guys strictly says it should be replaced with OEM sensor.
So, you replaced with ntk/ngk and problem solved, right? It also reduced your average consumption?

[oragex]

The O2 sensor only adjusts mixture on acceleration so mostly the city and heavy traffic mpg did increase, highway remained the same. There are discussions about using aftermarket sensors on Volvo as several brands can trigger a check engine light. The Ntk didn't on my car. The best is to remove the sensor and read the #number & brand (Denso, or other) and find it online for much less than what Volvo sells. Part number is important as a lot of online sites have errors when it comes to recommend a part for a specific engine.

[Marihuana]

Yeah, my highway is same, too. Heavy city traffic max 14 lt/100km.
I can get the part number from my dealer, that's no problem, but I hope online seller send the correct part. I found Bosch in my country with a cost of 50 USD approximately , but will keep searching.

[ThommyKent]

The O2 sensor only adjusts mixture on acceleration

Wrong my friend.

[Marihuana]

Guys, any idea about STC issue?