2001 tacoma backfire out of the air box

Idle control valve is screwed up making it run rich. ( had this happen before to mine)

Or your TPS is out of wack.

 

In many vehicle powertrain control systems I've worked on, 4K RPM is the transition from Mass Air Flow input to static Volumetric Efficiency table lookup for fueling. Don't know if Toyota/Denso use this breakpoint but it seems likely given your symptoms.

MAF actually reads the air quantity being fed to the engine, whereas the VE table values are static integers based on calculations from the factory...much less accommodating of glitches even in a closed-loop oxygen sensor fuel management system.

If you can get access to a scanner, get readings on Long Term Fuel Trims for Bank 1 and Bank 2 at various RPM/load combinations and report back. Get idle, steady cruise, uphill in a high gear, hard but not WOT acceleration through the gears, and holding at 4K RPM while the backfire happens. Report your numbers.

1.) Check to see if the LTFT numbers vary much between the two banks, there should be no more than around 5% difference between them at any given time.

2.) Check to see if they're ever > 10% or < -10%, even if they're closely matched between the two banks.

Post your data and let us know what you find.

 

Ive checked everything but the ECM. I guess Ill have to buy one

 

How often do you run seafoam through your engine?
Build ups of deposits can increase compression and cause pre-ignition problems. Running rich can have the same effect, but can be found with a smog test.

Please list the tests you have accomplished and the results. Saying you have checked everything but the ECM isn't going to help us give you any more constructive ideas.

 

checked the timing. Check the idle control. Changed plugs and wires. Tested all the sensors. disconnected all controls and everyone gets the code when i unplug them. Plug them back in code turns off. Checked all the injectors. This is the only reason I believe it could be the ECM.

 

Also replaced the fuel filter. I have not run any cleaners or boosters in it for awhile

 

An exhaust gas analysis will tell you if it is running too rich. Not sure if you have a smog test in your area, but a shop that does work for that will have one.
A vacuum test will show overall engine health, but will not show a floating/sticking valve at speed. It's worth doing, and a vac gauge is cheap.
A leakdown test gives more detailed info than a compression or vac test. It will tell you which cylinder has a problem. An inexpensive tester can be found here:
Work from the cheap to the expensive. Prove the ECM bad before you condemn it. That way you won't have a pile of used, working spares. That is a very expensive way to troubleshoot.

Let us know what you find. Happy hunting!

 

Oh yea, I forgot... Seafoam! Seafoam! Seafoam!

 

OK so here it is guys. The half moon that keeps the crank shaft and the pulley spinning as a unit gave out. This eventually caused the bolt that holds the pulley to come loose.This was causing the pulley to float out a bit and cause an issue with timing. So. Took it apart, replaced the half moon, and put it back together. GOT IT!! The truck is back to normal. Thanks to everyone who tried to help.

 

Yes Iroh. Even you