Less MPGs after tune up.

Hey guys, I'm having an issue with my MPGs. I did some tune up and maintenance work on my tacoma a couple of weeks ago, and I'm getting about 1.5 to 2 MPGs less now. I replaced the plugs, which I'm assuming are the originals. I bought the truck used, so Idk about how much maintenance the previous owners did. It has 127,000 miles on it. Anyways, I used the NGK and Denso combination that it came with, so same OEM plugs. I changed the air filter. Also changed the fluid in the front and rear diff, and transfer case. I rotated the tires as well. I was getting right around 16.5-17 MPGs before, and now it's dropped down to 15. I've also been a little easier on the throttle, so I figure that alone should improve it a little bit. Anyone else had this experience? Does anyone know what the reason behind this is?

 

Dirty throttle body.. I believe mine is the same I need to clean it too

 

It could just be your computer re-learning the new plugs. Give it a tankful or two and then check.

Did you go with a higher viscosity fluid in your rear diff? I'm going the lightest possible next time. I don't tow or drive hard very often.

 

Thanks guys. I feel like if the throttle body was dirty before, wouldn't I have been getting worse mileage before I did the tune-up? IlI' still clean it. It probably needs it anyways. Thanks for the suggestion. I have no idea what type of gear oil was in it previously, since I bought it used. I've only put about 15,000 on the truck since I bought it. I just assumed it needed to be changed. I put

$30 Mobil 1 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

Mobil 1 75w-90 synthetic back in it. I have heard about the computer needing to adjust. I'll wait a while and see if it changes.

 

I just changed my diffs and tc today.. Mobil 1

 

What’s this?

 

I don't know what you're asking about...

 

Tune up, do you mean just maintenance or some tuning (ECU)?

 

Just spark plugs and air filter, and the other stuff in the original post.