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Troubleshooting the secondary air sys. on my '98 was pretty straight forward. I could hear the air pump running at start up so that seemed good. I pulled the vacuum connection loose from the intake manifold and attached a hand held vac pump. Pulled 15" vacuum and let the thing sit for 20 minutes with no drop in vacuum, indicating the lines and tank all the way to the vacuum solenoid valve were good. Next I hooked up the Durametric and activated the system (if you don't have a Durametric or other diagnostic tool you can just apply 12VDC to the injection solenoid valve to see if it works.) Vacuum immediately fell to zero. Diagnosis=the diaphragm in the air injection vacuum valve has failed. If that valve was good and the vacuum solenoid valve was good the vacuum should have dropped slightly once the system was activated. If the vacuum solenoid valve was bad or not getting voltage then there wouldn't have been any drop in vacuum when the valve was activated. If the system holds vacuum, both valves are good, and the air injection pump is running then most likely the passages in the cylinder heads are clogged with carbon. This means dropping the exhaust manifolds and cleaning the passages out.
Hope this helps.
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