As I dimly remember when replacing ours, you need to remove the idler pulley, and that may be possible without removing the whole tensioner assembly. Be forewarned, though, that the tensioner function is due to torsion on the rubber cylinder of the the mounting bushing. If yours has never failed before, it is due, from the rubber deteriorating with age. Mine did, and the inconvenience of waiting for the new tensioner with the vehicle disabled convinces me you would be smart to do that now as well.

Steve

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'91 MB 190E 2.3
'08 RAV4 Ltd 3.5
'83 Lazy Daze m'home 5.7