I have been getting 12-13mpg recently. I just replaced oil and filter with Mobil 1 and changed rear diff. fluid. I have roughly 170,000 miles and I don?t know the timing belt history. The 4runner also feels like its lacking low rpm power. Could the timing belt be it or what else could it be?
Its a '98 4runner w/ 3.4L running 265-75-16 BFG all terrains.

 

Go buy 2 cans of SeaFoam. Take one and pour 1/3 of it into your main vaccum line. (Pop the hood and look to the far right on the firewall. You'll see a big black cylinder, the vaccum line is connected to the left side of that.) Have someone in the 4Runner giving it gas because it'll want to die. Let it smoke for about 15 seconds then cut it off. Let it sit for 5 minutes or so and cut it on. You'll pour smoke out your exhaust. Once the smoke is gone, do the whole process ONE more time. Then pour the remaing 1/3 of the first can and the whole second can in you gas tank. That should get you a few more miles under you belt.

 

Have you replaced spark plugs, plug wires, distributor cap and rotor? Also try cleaning your throttle body. Sea Foam is also a good idea.

 

Oxygen sensors..

 

I'm betting on the O2 sensor, too.

Has your driving habit changed? Are you mostly on the highway or cruise around town? Heavy foot?

 

not enough seafoam in the first post man.. if you decide to do seafoam do it this way. those 2 cans wont do much..

2-3 cans in the fuel tank with 4-6 gallons of gas. run till empty THEN

1 can of seafoam through the pcv valve or vacuum line. use intervals of 1\3 of a can let it sit in there for over an hour.. do that 3 times (hence the whole can in 1\3rds) i promise you will see a big difference..

THEN change the oil bc you just saturated it with additives

 

If you run it through your PCV Valve, you'l have to change your oil. If you run it through the vaccum hose you wont.

 

how is that? what is the difference? just curious

-- ifyou put that much in your tank you should changed the oil.. ALL fuel additives will spike contaminants in your oil.. you should do all of this prior to an oil change

 

Running it in you vaccum hose, i thought, only Put seafoam in the top half of the engine. This is what I was told at Autozone.

 

+10000

 

I don't see why you would have to change oil because you used the PCV valve. It just gets sucked into the intake, just as it would if you put it in the vacuum line. In fact, your PCV is essentially a vacuum line right?

There should be no way for it to get into the oil unless you dump it into the oil. Someone correct me if I'm wrong.

 

I did sea foam a few months back. The plugs have been replaced and one coil pack that went bad.

Correct me if im wrong there are 2 O2 sensors, how do I know which it might be?

 

If your O2/air fuel ratio sensors are bad, they'll turn your check engine light on. Then you can hook it up to a scanner and it will tell you which one is bad.

 

Yes ,your correct. The PCV re-curculates oil vapors into the intake to be burned off with the combustion cycle. The PCV is indeed a vacumm line and there is n need to cahnge the oil after adding it there. You will however have to change the oil if you add Sea Foam into the crankcase.