I replaced the timing belt and water pump on my 2000 Honda Civic EX, auto trans.

Now the idle is a bit rough--it'll sound fine and then stutter and then the revs will pick up for an instant and then it'll run fine again. In drive with the brake on, the car shudders badly and even stalled a couple times. I adjusted the spark timing which helped slightly (looking at the marks on the flywheel). But it's still bad. (I'm thinking when I sort this out I should put the timing back where it was--but I only moved it a hair.)

I checked and rechecked the timing belt timing before putting it all back together. I also found that I could slip the belt one tooth or another by taking off up the upper cover and taking the belt off, moving the camshaft, and putting it back on. I tried that going one or two tooth either way and so on. That didn't help.

What's left is that the timing belt seems to move back and forth a lot. When I loosened the timing belt tensioner as part of the tensioning process the tensioner didn't seem to move.

Would a slightly loose timing belt cause these symptoms? It's not skipping any teeth.