Backfire/Studder under acceleration

CONGRATS!!!!! I was secretly hoping it was something else. I have a similar issue! having 2000 4runner 3.4 motor. Replaced air box,(potential stripped screw on the MAS) replaced MAS, Replaced TPS, replaced IAC, Replaced ECT, Replaced brake booster ( as per Dealer diagnosis) , checked vacuum lines for breaks. New plugs. No codes. Been to 4 shops, all the incorrect diagnosis. The problem is exactly the same and has not presented itself differently after each repair.
Runs fine on start up. As it approaches normal operating Temp, it will seem to lose power. If you come to a stop and accelerate it bogs down, back fires through the air box. Does the same thing if restarted after 30 minutes. When the issue occurs , if you pull over and restart the vehicle it will return to normal operation.
Again.. CONGRATS!!! and get a Lawyer to talk to that shop! LOL!
 
This should be a sticky!!!

Glad I found this and am praying it will solve my issues. After searching and searching I too decided on injectors. Did plugs, injectors, fuel filter, maf. Looks like the cps is on my to do list. I am hopeful for the first time in a while.
 
BFEATHER2008 said:
I am a toyota mechanic and id say get ride of those crappy plugs i stick with oem plugs and wires. I had aftermarket plugs and wires in it when i bought the teuck and it misfired and studdered on acceleration. I replaced plugs and wires and bam its fixed. Then it stated misfireing again later down the rode and had to replace a coil. Id would say start with new plugs oem preferred but if not get only denso or ngk plugs due to the fact they are what comes from factory from toyota. And with the CEL flashing then going off is overheating the convertor. If you drive it drive it easy cause you can melt your CAT and if you do that OEM CAT is 1600 bucks. So just beware and drive with ease. Like i said start with new plugs first if its still there replace wires if its still there which i doubt it will be it would be coils. I really doubt it has anything to do with fuel injectors. I have never replaced any fuel injectors. My dad is also a toyota mechanic of 32 years and he has barely if ever replaced an injector. They are one of those parts that seems to never fail on toyotas. Good luck on the truck hope you get it fixed. And try to stay away from plugs that arent ngk or denso. Every car that comes in with a misfire code at work we always check the plugs and they seem to always be aftermarket plugs and we put OEM in and it fixes them.
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having same issue with hesitant as not getting air/gas codes p3511 , replaced gas filter - if replace sensor was told have to replace all sensors
 
2001 Toyota 4 Runner

I replace both catalytic converters, muffler and tailpipe 6 weeks ago due to sluggish ride, back fire smell. Improved a bit but not fixed, replaced spark plugs with NGK and wires (carq?) much better riding smooth.
then needed new ignition switch - easy repair.

now all sudden running sluggish tacking high when accelerating but not really going anywhere. once get driving staedy seems fine til have to stop and accelerate again --
replace gas filter and added fuel injection cleaner to gas tank , cant say made any much better if at all. Could it be 02 sensors due to catalytic being replace or could it just be plugs(after month old) and if replace 02 sensors a/f near or connected catalytic do I or should I replace others, as was told one will sense other then fail .
 
Trid Del said:
I replace both catalytic converters, muffler and tailpipe 6 weeks ago due to sluggish ride, back fire smell. Improved a bit but not fixed, replaced spark plugs with NGK and wires (carq?) much better riding smooth.
then needed new ignition switch - easy repair.

now all sudden running sluggish tacking high when accelerating but not really going anywhere. once get driving staedy seems fine til have to stop and accelerate again --
replace gas filter and added fuel injection cleaner to gas tank , cant say made any much better if at all. Could it be 02 sensors due to catalytic being replace or could it just be plugs(after month old) and if replace 02 sensors a/f near or connected catalytic do I or should I replace others, as was told one will sense other then fail .
Click to expand...

It could be transmission issue if the engine is reving but poor acceleration. check the atf fluid level at operating temp also check for color and burnt smell.
 
So I just read every single reply to this post, 16 pages worth in hopes that I would find the solution to similar issue I am having. BTW, GLAD THE OP GOT IT FIGURED OUT!

My stuttering/loss of power and backfiring occurs about 3,000-3,300 RPM but only under moderate to heavy exceleration, not WOT throttle condition. The issue is really throttle position dependent but only in that RPM range. For instance if I put it in first gear (automatic transmission) and I accelerate up to 3,500 RPM and back down to 2,000 RPM I can continually do this over and over with no symptoms. The same is true for 2nd gear. Now if I accelerate at WOT the engine quickly and smoothly covers the mentioned RPM range without any detectable stuttering/loss of power or backfiring. The issue really only occurs under a load at the 3,000-3,300 RPM range under moderate to heavy exceleration, not WOT acceleration. I am also NOT getting a check engine light. So far I have cleaned the MAF sensor. At first I thought it could be a dirty fuel filter but the engine performs fine under WOT.

So, does anyone have any thoughts? Thanks in advance!
 
constant back fire

hey so I am new at this whole forum thing. I've got an 99 limited, i just replaced the wires, coils and plugs, now it doesn't miss fire like it did but it back fires constantly and smells rich?, there are no codes in the system now, before it had miss fire codes but they are gone. also, before it just misfired but no back fire, now it backfires constantly, but it seems to run better, what should i do? all suggestions are welcome
 
simonk said:
hey so I am new at this whole forum thing. I've got an 99 limited, i just replaced the wires, coils and plugs, now it doesn't miss fire like it did but it back fires constantly and smells rich?, there are no codes in the system now, before it had miss fire codes but they are gone. also, before it just misfired but no back fire, now it backfires constantly, but it seems to run better, what should i do? all suggestions are welcome
Click to expand...
Sounds like you have a couple of the spark plug wires in the wrong spot
 
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