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1991 Chevy S10 failed smog check at idle but not at high rpms.

My Chevy truck passes basic smog test at higher rpms but not at idle for the California basic smog test. My maintenance book says the EGR valve does not work at idle on a computer controlled vacuum solenoid in park or neutral, but will work in drive, in park at higher RPMs the EGR valve will work. DMV assigned this vehicle a basic smog test and this truck has failed twice at idle in park and has passed at higher rpms when the EGR was working. I told the last shop I wanted my Chevy S10 enhanced smog checked. They said okay, but after the test they didn't smog it on the dynomometer, they just did the same as the first test (basic smog check) and of course it failed again with no egr. My question is, how do I get a dyno smog inspection so my truck will pass?
Answer:

Not much we can do to get the DMV to require an Enhanced Smog Check on your 1991 Chevy S10. For whatever reason, whether because your Chevy is register in a "Basic Smog Check" area, or it's emission test results in the past have been good enough to where you don't need a test only smog check facility, you'll need to get your S10 to pass the basic smog check. We'd recommend you find out why it is failing the idle speed portion of the test. Are HCs or CO too high, and why? posted by SmogTips Support

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