Hi Guys, 99 4runner v6 SR5, recently bought it. 160 thousand miles on it.

Has had a recent tune up, cleaned maf, new plugs, wires etc.

First problem: Seems to lose and gain power. For instance, on the highway under moderate to hard acceleration it will go pretty steady in 2nd gear and then around 4500 rpm it suddenly gains a noticeable amount of power. From a standstill, it seems to have power one time and less power the next time.

Second probably related problem: HORRIBLE gas mileage. Around 8-9 MPG, calculated the proper method. It's the average over 3 tanks of gas since I owned it.

I do have a code checker and live data scanner, it has no codes, TPS reads fine, MAF reads fine, o2 sensors read fine.

Totally stumped here since it doesn't throw any codes. Do I throw in a new cat and hope that fixes it? Fuel filter is lifetime right?


EDIT: Let me say one more thing, it's extremely cold where I am, ranging from -5 to -20 Fahrenheit, so 8-9 might seem unthinkable, but I'm positive part of the horrible mileage is due to the cold and winter gas, but something is still wrong somewhere.

 

There is definitely a problem!

These motors are pretty good so, I wouldn't expect it to be anything major. Putting a new cat in would be one of the last things I'd do.

Obviously the mixture is very rich. It might be trying to overcompensate for too much air in the system. The O2 sensors might very well be causing a problem. Have you tried disconnecting 1 or 2 of them and seeing if the truck runs better?

Have you tried cleaning the throttle body? Check for vacuum leaks? I don't think a can of seafoam would fix your problems, but might help a bit. Seafoam throught he PCV hose into the intake does dissolve carbon buildup within the intake plenum and pistons.

Fuel filter sounds like another possible problem. They aren't really lifetime. Something thats easy to change and cheap, go for it. Hopefully someone else chimes in, I'm not too familiar with the 3.4L and having bad gas mileage like that.

 

Jesus really? jump to a cat change? ^ is that just because of the mileage?

to start out with that will make a huge difference that im sure it will cure your problem is pull out your mass air flow sensor. disconnect your battery first. get some cleaner for it. don't touch the wires. spray that bad boy down and get all the dirt/grit and grim off of it. don't touch it though. not with your fingers. really just don't touch it. spray it clean let it dry and then re-install. and enjoy.

thats probably where you mileage is getting killed. probably have a cotton ball of crap on the thing. and if the guy ran a K&N air filter on it and over oiled it (happens often) you could have that sensor coated in oil.

start there and report back before dropping any money on it quite yet.

 

I suggested a new cat change because I've already done a whole tune up and cleaned the maf already. When I took it MAF out the wires were still silver and not dirty but I cleaned them anyways.

But there seems to be plenty of exhaust coming out the tailpipe so I doubt the cat is really clogged bad, if at all. I just don't know what to check next and it's costing me a fortune in gas while I drive it

Only thing I can think of is fuel filter or injectors but then why wouldn't it throw a code?

 

My 22RE seems to do the whole, gain power loose power thing...
I still havent figured out why....
But dissconnect one of the oxygen sensors and take it for a drive see if you can tell a difference.
Also, make sure its not hanging around where your driveshaft can snatch it up...That wouldn't be fun at all....

 

I just saw you mentioned 4500 RPM. I don't know if I've ever been able to get my 3.4L to 4500 RPM!?

 

Well I don't normally take it that high either, but when I noticed the acceleration problem while city driving I decided to take it on the highway so I could safely see what would happen when I stayed accelrating for 10-15 seconds or so. (Moderate acceleration from 0 to 70 mph, and it loses and gains power several times like I said, but it's NOT like a misfire or a "blip")

 

I hate to suggest it but:

Take it to the dealer and have them put it on their engine analyzer. I don't always trust aftermarket code readers.

.

 

don't you mean take it to a Toyota mechanic and hook up a Techstream ?


OBD II is OBD II and unless someone hooks up a Toyota Techstream, all you will get out of it is OBD II data and perhaps exhaust gas analysis...the question is 'how sophisticated is the OBD II tool that is going to be connected ?'

 

Other problems don't seem like problems, but rather normal behavior. The mileage is a little questionable, but still within reason. How long/short are your trips? What is the average speed? If you are driving over packed snow at 15mph all day long, you'll get 8-9 no problem. Have you blocked off the radiator and the whole front with a blanket? You are probably not even getting up to operating temperature, ever.

 

No, it's not blocked off, and before this I had a 89 4unner 4cyl which I took to work and back getting 15-17 mpg. It was totalled, and this 99 4runner replaced it and going the exact same route to work is getting 8-9 MPG.

And for perspective, I also have an 88 V6 on 35" tires, stock gears, lifted. And I get 10 mpg which is expected given the mods.

So thats why I'm so confident that something is wrong somehwere because I'm getting worse mileage on a stock 3.4 than I am on my big truck with 35" tires and stock gears lol.

And I have a scanner like I mentioned, which shows Live Data. If anyone knows any telltale signs to look for let me know!

 

Well how about this, after sitting overnight, how many minutes does it take to get to 190F water temp via ODBII?

 

bad thermostat perhaps

 

Great... Finally threw a code. P0303 Cylinder 3 Misfire. So searching for that code I came across:

https://www.yotatech.com/forums/f2/s...ebuild-204790/

The guy in the above thread got a "carbon cleaning" done which apparently fixed his problem. He was also getting horrible mileage.
Should I have toyota do this carbon cleaning or buy a can of seafoam myself and run it through a vacuum line?


**And thanks for everyone who responded so far I appreciate it!**

 

Ah so it was a misfire!

You can buy seafoam at most autoparts stores. Its in the fuel system cleaner areas. Comes in a can.

Where the PCV valve is, you disconnect the hose going to it. It will have a high vacuum, and you can pour about 1/3 of the can in there SLOWLY. Turn off the car for about 20 minutes. (Have the car warm when you start in the first place, it stays alive easier). Then when you start it, it will billow white smoke for a bit.

I would also test the coil's resistances, outlined in the factory service manual.

 

Fixed my misfire, it was a bad coil (bought a used one for $30), after that I also got a carbon cleaning done on the injectors. Replaced the PCV too.

Still has horrible mileage though. About 10-12 MPG. No other codes, runs real smooth now with the "new" coil. So really no symptoms just horrible mileage.

So.... 3rd Gen owners, whats the deal? Need some more suggestions!

 

Just FYI, I get 17mpg, all hwy, on my 1999 3.4 4runner. The winter gas is killing me. I get 19 mpg in the summer.

Sounds like you're doing the right things. Only other suggestion is spark plugs?

Also, if your fuel filter is not too rusted to change, I would do it now, just do it while you still can. Mine is so rusted that two toyota dealers told me they can't change it. Of course, they told me it was a lifetime part....after they failed to remove the current one.

 

Did you seefoam it after you replaced the coil? If so did your gas mileage increase any?

 

Make sure you have reset your computer after your coil pack change. It may still be calibrated for your faulty condition.
I usually pull my EFI fuse from under the dash. Leave it out for a couple of minutes. Or take off and touch your two battery cables together for 30 sec if you are in a hurry and are under the hood already.

 

Replace your plugs, wires and reset your ECU by unplugging the battery then step on the brakes to purge the system of any remaining electrical power. Give your ECU about 100mi or so to correct itself then check your mileage.