I have a 98 tacoma 5 speed 3.4L limited 270K miles and the past few months at 3500 rpm stationary or in gear it sputters and backfires. Checked and cleaned plugs, cleaned MAFS, removed cat and ran it, cleaned fuel filter, new gas, cleaned throttle body, and PCV. Still running the same way. No CEL but every now and again the check engine light will come on and when I try to pull the codes it will do nothing and then i turn it off and back on then the CEL is gone. So random. And MPG went down hill I believe as well. Have been searching for ever it feels like to find a solution and have heard some people fixing it by different ways. But the cards don't seem to be in my favor on this one!

 

Please not the knock sensor (more likely wiring, if it's that). That should trip a cel, though I've heard of a couple that have not. Not a mechanic so take this info with a grain of salt.

 

I've read some people say it could be the knock sensor but haven't really had the time to check it out and when I do, the weather is crap. And I can't afford any parts really right now. At least in the couple hundred dollar range. I know that sensor isn't that much but my luck it's the most expensive part that is messed up.

 

IF it's the knock sensor circuit often times it's the less than $20 wiring harness that gets brittle where it is between the lower intake and the head. Sometimes it's the much more expensive piezoelectric sensor.
I have seen some (but not enough) info about using Radio Shack sensors in a more accessible spot and also something about someone doing a splice job to fool the 'puter. May bear some looking into those possibilities if that turns out to be your particular woe.

And bump for other ideas on the problem.

 

Have you checked for a vacuum leak? Intake tube, vac hoses, throttle body gaskets, etc....

 

Ya I have checked for leaks, haven't found any. I read one guy's post and he nailed it to the t with all the same problems I'm having and ended up being a loose crank shaft pully. Never would of guessed haha. He said the wobble from it threw off the timing at higher rpms and I just had the timing belt and water pump replaced and pretty much everything on the front of the motor. Belts, alt, radiator, hoses, head gasket on one side cause I blew it. Had heads re shaved. I have done a lot of work in this truck.

 

Would not have thought of that one either. Is the torque on the crankshaft pulley bolt supposed to be 217 ft lbs like the 3.4 4Runner?

 

No, I just checked the my book today and it's 185

 

Seriously double check that number....I think that's a used-to-be spec...pretty sure it's supposed to be 217 ft lbs for the 3.4...

 

Ya I got my Hanes manual right in front of me, and ya it's actually 184 for 3.4L 95 and up. Crankshaft pulley bolt.

 

Double check it in something beyond a Haynes manual, and something newer. I think it used to be something like 184 but has since been changed. I know my 96 3.4 is 217 ft lbs and I'm pretty sure the same goes for the Taco and T-100.

 

OP, habanero is correct with the 217 ft-lbs spec for the crank bolt on the 5vz-fe engine.

Toyota initially listed the spec as 184 ft-lbs and then changed it to 217 ft-lbs in about 1999.

 

Ok ok, don't gang up on me now haha jk. But thanks though. I'll have to check on that and see if that fixes it.

 

Not ganging up on ya at all. Just a bit of reinforcement.

 

You were dancing with the right partner, just they changed the dance card on you, is all.

That Toyota did that makes one wonder, I know there's been more than one loose crank bolt and thus pulley. If it turns out to be your problem and you've found it soon enough pat yourself on the back for job well done and disaster avoided.