I’m having a problem with my 2016 is200t. I don’t have much done do it just a injen intake and a throttle controller. With these mods I usually hit around 20-23 mpg driving like I always do and my car is quick and jumpy and has very little lag. Started three days ago I saw that my mpg was all over the place sitting at as low as 11 mpg and my car felt a lot less quick and a lot more laggy. I checked my intake to make sure there was no leaks or something wasn’t fitted right and went and retightened and took my air filter off and cleaned it even tho it’s brand new (not injen air filter but a K&N Filter https://a.co/d/7vBFrQ2). Drove it and it felt back to normal. Then couple hours later driving it again it was doing the same thing dropping down to 13 and car felt less quick. MAF sensor?? Maybe needs to be cleaned/replaced? Not really sure anyone have any insight ?

 

Are you going based off the reading on the car? or you're doing the actual math after a fill up? (fill up and calculate your mpg)
My 2017 IS200T had that problem. The reading was completely off (but the math was right), it was the FRAM air filter that caused all of it. Switched out to K&N and it started reading properly again.