I noticed an open vacuum port on the intake manifold (4L stock Cherokee) so looked for and found an unattached hose that seems to match. Unfortunately plugging in the hose immediately kills the engine. Plugging the vacuum port with my finger does the same thing. This seems odd to me as the engine seems to run fine with the port open and no check engine light.

Thanks for any direction on how to proceed from here. Pics below:

This is the open port:

Open port is a bit left of center

This is the hose I dug up that seems a likely match.

The free hose I found leads to the bottom line on this canister thing on the passenger side of the firewall

 

That elbow looks like the right one to me.

 

On my 2000 it is connected to the manifold. I'm not sure why it would cause your engine to stall immediately, so I can't help there but you are correct that it should be connected.

 

The fitting and hose feeds the canister purge solenoid and/or the leak detection pump. Have you connected the hose, then restarted the engine? I'm assuming the leak is being compensated for by the IAC valve and it can't react fast enough when you first plug it in.

 

Thanks! I was more concerned why the engine ran fine with the port open then faltered when I connected the hose but apparently that is normal behavior. I replaced the brittle plastic hose with regular vacuum line then started the jeep and it runs fine. Apparently a lot of jeeps have a plug over that port but some like mine have a leak detection pump connected to it and it is not uncommon to fall off. It should have thrown a code to trigger the check engine light but not gonna worry bout that
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Thanks! Spot on and things suddenly make sense! My first response was to a page I had left open and had not seen your comment until after I replied

 

Thinking you are wrong on that. That is is the middle nipple (port) right?
Pretty sure all Jeeps have that with a vacuum line attached.
The same with the one nearest the firewall.
It is the one nearest the radiator that could have a hose or be capped.
Capped indicates you have '00 with Federal Emissions. If there is a hose attached to it means CA Emissions.

 

I could be mistaken. It looked like the same port being discussed in another thread but I just saw two ports on mine. Entirely possible I missed one