1999 Tacoma 2.4 5 speed awful gas mileage

Hi all, I have a 1999 Tacoma 2wd Regular Cab 2.4 with a 5 speed and it seems to be getting awful fuel mileage. If the gauge is accurate Im averaging 12-14 mpg. The engine is throwing a lean code, which I originally thought to be MAF but after replacing it twice it keeps coming back. I also recently cleaned the throttle body and checked for vacuum leaks, which warranted no answers. Tire size is 235/75/R15

 

What's the actual code it's giving? That may help people be able to provide some additional suggestions...

I average almost 25 mpg with my 2.4 5 speed so 12-14 is terrible!

EDIT: Is that tire stock height? Have you accounted for the difference in tire size from stock to what you're currently running?

 

Specific code is P0171 Lean in Bank 1, the truck has been lifted 1.5 inches in the rear and 3 inches in the front to level it out

 

There's your answer!

 

Go buy yourself a can of starter fluid and while the engine is idling, squirt little bits of it around the intake manifold. Doesn't take much (you're not spraying flies ). If there is a vacuum leak the idle will speed up noticeably. If it does, then carefully squirt an even smaller bit right at the vacuum hose connections until you narrow it down to one particular one. You'll know if you found a leak. Replace the hose, or put a clamp on it. Not all of the hoses have clamps.

If the idle doesn't speed up when you spray around the intake manifold, then follow each tube from the engine to wherever it goes and spray at that end. That's what I did to my engine when I got a lean code. I found a vacuum hose that went into the throttle body. Didn't seem loose, but I put a clamp around the end, started the engine, sprayed around it again, and the leak was gone.

If you are sure you don't have a vacuum leak, then I would suspect an injector has gone south.

 

Does a O2 senor really hurt gas millage that much?

 

Sounds like that is my new project for this afternoon. I've been having poor gas millage issues as well and I know my upstream O2 senor is bad

 

No it’s not

 

My 2.4 5spd gets about 25mpg as well on stock tires.

Do you know if you replaced the maf with a Toyota friendly brand? I’ve read multiple places where guys have talked about these trucks only liking specific brands of sensors. I can’t remember which they recommend though and can’t seem to find the threads to link to at the moment. Maybe someone else here knows.
If memory serves me correctly, new O2 sensors would be cheaper than a friendly maf.

 

I also have a 2.4L 5 speed and get about 25mpg as well ( seems to be the consensus). I had the same issue with the upstream O2 sensor, and even after replacing it I was still getting a code. I got the URD O2 sensor box and that worked well.

 

P0171 is almost always a vacuum leak, start looking for those. If you confirm there isn't one, then maybe a bad air/fuel sensor or bad MAF but you said you replaced that already.

Did you use a Denso MAF? If you used a cheap aftermarket one then that could also be causing the code. Toyota's don't like aftermarket sensors.

A lean code will 100% ruin your gas mileage so you need to get that figured out if you want your MPGs to go back up