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Toyoto Corolla (1992) fails Smog Check in California: EGR valve or Intake Manifold Responsible?

My 1992 Toyota Corolla All-Trac just failed the functional part of the smog test in California: when vacuum is applied to the EGR valve, the engine does not rough as it should. The question is: is the test tech’s explanation of why it failed plausible? He insists that under such circumstances, 99% of the time, the failure is not in the EGR valve itself but in [the connection from the EGR to] the intake manifold, which he says must have become clogged.

I am skeptical for a number of reasons: chief among them being his Vietnamese accent is so thick I can’t always tell what he is really trying to say, yet he is the one who gets impatient (answering questions with “I know what I am doing”) when I don’t understand him.

Yes, the passages to and from the valve can become clogged, especially with a lot of short stop-and-go trips.
Often the valve is mistakenly replaced.

Thanks circuitsmith. But I have to admit: when I saw the placement on the EGR valve, I thought the connection to the manifold was much too wide (about 1/3 to 1/2 the diameter of the EGR values itself, 3 inches) to get easily clogged. And do you have any idea how common this is?