The tensioner shouldn't move backward, it is a ratcheting mechanism that locks as it "clicks" forward in increments. Sounds like yours is worn out (and may be part of your cam lobe problem?). Though it may have some system of lubrication, it moves forward, as slack allows, by spring pressure only and needs to be reset any time the chain is deliberately slackened (like, by removing the cam gear for example).
To reset it, it must be removed, the pin should be pushed forward through the barrel and placed back in the front again. When you put it back in the car and push the screw cap back in/on, the spring pressure will cause it to seek its own proper adjustment.
When put back in, make sure all the chain slack is on the tensioner side of the cam gear and the other side is somewhat taunt.
Failure to reset it could cause the chain to break in short order.

Also, while you're in there, check the condition of the tensioner rail and chain guides. If the tensioner rail is worn down to metal or moderately scored it should be replaced.