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I have heard that since I owned the car maybe 10 times on random start-ups... Never heard it on the new pump.
Just found this on RennTech.org that may be what I'm looking for:
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"I had a problem with my secondary injection and it turned out to be the change over valve was not working."
This is by far the most common cause, especially if you can hear the air pump working. The change over valve has a vacuum diaphragm which goes bad. You'll find this valve under the intake manifold on back 1-3. You can test it by applying a vacuum and seeing if it holds. If not, you need a new valve. However, usually the change over valves failure is a symptom and not the real problem. A lot of times what happens is the non return valve (which prevents exhuast from the cylinder head going up stream to the secondary air pump) has failed and the exhuast has burnt up the change over valve. If you see corrosion or scorching on the one end of the change over valve, it would be very wise to replace the non return valve.
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