As asked for above, about all the charcoal canister can do wrong is be a vacuum leak. A defective tank system can cause fuel to pass through the cannister, but that wouldn't be the cannisters fault.

For diagnostic purposes the thing should be isolated to prove that the idle improves.

Sounds like guessing to me.

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Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician