Tacoma 3.4 v6, 250,000 miles. last smog 2 years ago barely passed the low idle HC, this year it failed the low and barely passed the 25mph test? I can attach actual readinsif that will help?
Hydrocarbons (HCs) are unburned fuel. You may need to replace sparkplugs and wires, if this has been done or doesn't fix the problem you catalytic converter may be worn out.
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SOURCE: engine rough idle cold. passes smog once temp reaches thermostat
you can take apart the top section and blow out the small passage that's bellow the throttle plate.
SOURCE: high hc
you may need replace the catalytic converter, but 1st do this, clean the throttle body and idle airbypass valve, change the oil before the retest as well, get it as hot as you can before the test, hold it at a high idle prior to the test, this may squeak you by, as a 20 year smog tech these are the thing I did, if all else fails do the cat conv.
SOURCE: ASM 2525 NO ppm TAILPIPE EMISSIONS failure
have you had the the engine codes pulled and reset?
and if so what are your engine codes?
i dont know of any car that will pass emissions test with the engine light on.
we cure your trouble that caused your engine light to come on and you will pass your test.
later
paul
SOURCE: My 1991 4runner failed emissions test with high CO and HC levels.
Not sure, but did you replace the oxygen sensors. Is your catalytic converter still good?
SOURCE: Having a problem passing a smog test on 1996 Toyota 4Runner SR5 V
NOX is produced when cylinder temperatures exceed 2500 deg. The systems in place to reduce NOX are EGR and the catalytic converter.
If the number is only slightly higher than avg then I would suggest the EGR, make sure that any vacuum lines are attached and that the diaphragm moves freely, be sure not to damage the rubber inside the EGR.
Retake smog test, if numbers still out of range replace the cat.
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