AIC RENAULT MEGAN VALVE PHASE I

Good day,
due to a problem I had taking my car for its emissions test, I want to share this experience and explain how the situation was resolved.
When I took my Renault Megane Phase I for its emissions test, it failed because the CO reading was 1.83, and the standard states it should be below 1.83; it was 0.83 over the limit. The hydrocarbon (HC) readings were 563 at idle and 600 at cruising speed. They told me I needed to tune the engine, so I cleaned the injectors and the throttle body, changed the spark plugs, cleaned the sensors, changed the air filter, and took it back, thinking the problem was solved. To my surprise, when it was tested again, the CO reading was 0.83, meaning it had improved, but the HC readings were still well above the limit, although the emissions had decreased slightly. I took it to a shop, and upon inspection, they found that disconnecting a vacuum hose leading to the AIC valve changed everything. The HC readings started to decrease, although the engine revved slightly, reaching 1000 or 1100 rpm. After a while, they would drop to 900 or 800 rpm and then rise back up to 1000. After passing the test, I reconnected the hose, and with the certificate in hand, everything returned to normal.
Is there anyone on this forum who can enlighten me about why this happens and why disconnecting that hose alters the vehicle's HC readings?
I appreciate any information you can offer.

Greetings from Colombia!

By disconnecting that hose, you're likely letting extra air into the manifold (not being detected by the MAP sensor or mass airflow sensor), which is why the RPMs went up to 1000 or 1100. This leans out the mixture by introducing more air, so I think you might have a problem with the catalytic converter (if it's faulty, the lambda sensor tries to correct the mixture) or the MAP sensor (or mass airflow sensor, whichever it has) is giving an incorrect reading. It would need to be checked, and we should get other opinions. Cheers!