Hi, had this car in today with high emissions and irregular running faults. Split air inlet hose between air flow meter and throttle body was replaced which improved running.
Smoke-Pro'd the inlet to confirm it was now air tight.
O2 sensor at idle and fast idle was stuck at around 0.8v, so it's rich, and confirmed by O2 integrator at -21%.
Gas test showed 0.5%CO at idle and 3.5% at fast idle.
The inlet manifold valve located at the outer end of the lower part of the manifold was making a noise like a reed valve and I could feel it resonating, I sprayed carb cleaner around it to see the CO increase slightly. I then removed it and checked the vacuum pipes and diaphram with Mityvac and it all checked out ok.
This is the first time I have looked at one of these, how exactly does it work? Is the unit underneath it its own vac motor and reservoir?
I then refitted it and ran the engine to see that the O2 sensor was now working perfectly, the gas readings were all perfect and it ran really smooth and drove well. The noise and resonating was much less as well.
What could I have done? Are these inlet manifold valves normally an issue?

Sorry for the long post, thanks, Martin.