dumb ? about the vacuum cannister

ok i have an 88 xj. for the longest time ive been having idle issues. high idle, along with random start ups where the rpms jump up to 2000 rpms and then go back down.

normally the rpms at idle in gear are around 900-1100. in park/neutral 1000-1200

ive tracked down any vacuum leaks i can find. the thing about the cannister behind the bumper (which i relocated to my engine compartment) is that i replaced it with a known working one from a junkyard. (i disconnected it from the donar vehicle and it was still holding pressure)

i installed it and it immediatly dropped my idle to a lower rpm. next day it was right back up to where it was to begin with. there is no leak in the cannister. ive been spraying brake cleaner all over the place trying to find leaks. found one on the small hose that goes into the cannister and fixed that. no change though. didnt seem like there was any vacuum leak comming from that anyways.

my heater vents dont even work. everything comes out the defrost vents. doesnt matter what rpm. (although rpm used to affect it)

can the cannister go bad? doesnt seem to hold air like it did at the junkyard. does it matter which way its installed? from trying different things im sure the hoses may be plugged into the wrong side by now. but either way it doesnt change anything.

please help. this is a never ending problem.

Definitely sounds like the vacuum canister isn't working. The heater vents are a dead giveaway.

Are you sure the vacuum line going to it isn't cracked? If you're sure, I'd say the canister is junk.

well i put the cannister in, it fixed the idle. then the next day it was right back to how it was before. ive found other leaks but have since fixed them with no change. is there any way my jeep could just be eating the cannister up? like if there was something my jeep could be doing to make the cannister not work?

Check the vacuum-connector on the intake manifold. I had the same problem with everything controlled by vacuum. Looked everywhere for leaks, but it turned out to be that connector being clogged. Unscrew it and check it for dirt.