One is a air flow or temp sensor and one is a breather that recirculates fumes. The rule of thumb is to inject the hydrogen into the air inlet just before the air filter. You could drill a hole in the pipe just before the filter and install a barb. It is a good idea to run it through your cars air filter so the hydrogen is circulated to all cylinders evenly and its one last scrub before entering the engine.
Hi,
Thank you for this information. I did not know that the HHO gas could pass through an air filter
Best Regards
Remi