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Failed Smog Test High NOX at 15 MPH but passes at 25 MPH?

Tiny
ROYBOY59
  • MEMBER
  • 1997 TOYOTA 4RUNNER
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 156,000 MILES
I failed the smog test.

The NOX reads high at 15 MPH but passes at 25 MPH. No check engine light. I replaced the spark plugs and air filter before I took to Smog test.

I was told to clean the Mass Air Flow Sensor. I have never cleaned before.

Does this sound correct or are there other problems to look for?

Last year the check engine light came on but went out after two days.
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Monday, August 23rd, 2010 AT 9:22 AM

3 Replies

Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
A problem with the EGR valve not opening will increase the Nox-oxides of nitrogen
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Monday, August 23rd, 2010 AT 9:27 AM
Tiny
ROYBOY59
  • MEMBER
  • 1 POST
This Vehicle does not have an EGR valve.
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Monday, August 23rd, 2010 AT 9:55 AM
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
Knox is caused by high temperature in the cylinder vehicle does not have EGR that’s what it uses to cool the cylinders down the only other thing is lots of carbon buildup in the compression is higher than normal
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Monday, August 23rd, 2010 AT 4:21 PM

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