All of the videos about installing a catch can have the input (to the can)
hose connected to where the rubber hose on the oil filler just below the oil cap is connected.
When I checked this hose with the engine running it has a strong vacuum. Is this right?
If I leave this hose open the engine runs a little rougher. If I bloc it, the engine smooths out.
The output from the catch can is connected to one of the three
connectors on the large rubber (accordion) hose. But I can not decide which one to use.
And, do I block off the hoses that are left disconnected??
The engine runs great, no problems with cold start or hot start.

 

You can't leave any hoses open on a MAF equipped car. That includes a catch can that vents to atmosphere. That's why it runs rough when you do, so either connect them correctly or block them. But there aren't really any "extra" hoses, so nothing should be blocked if the intake is stock.

The hose pulls vacuum because it's connected to the intake. It doesn't matter which nipple on the accordeon you use, they all lead to the same place . Logically you'll use the one that went to the oil fill neck.

 

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I'm in the process of installing a catch can. It's not clear as to which hose
on the "accordion" hose to connect to the out put of the catch can?
And what do you do to the hose that was connected to the oil fill tube??
Where does the hose that was connected to the oil input pipe go?
And way does it seem to go toward the back of the engine if it goes to the accordion assemble/hose?
None of the videos i can find show you what to do with the hose/hoses you disconnected????
I can't believe that the hoses would be left open??
I guess I'm asking which hose comes from the oil fill pipe to the accordion hose??
..

 

https://www.rx8club.com/series-i-tec...iagram-214910/

Note the "catch can" inserted into the Mazda diagram. Your hoses should be routed as shown, if they're not for some reason, fix that.

I'm not sure which hoses would be left disconnected, everything is connected. But you're right, leave nothing open.

It doesn't really matter which of the accordeon connectors you use, thry all lead to the same place. But for packaging and ease of routing preformed hoses, do it as shown in the diagram.