Question
I have three zones, and zones 1 & 3 work fine.  When zone 2 comes on, it only dribbles out water.  However, it does start/stop when it is supposed to.

I made sure all the sprinkler heads were clear of debris.

Any ideas?

Answer
You have a restriction somewhere, have you checked the control valve? Do you have a lot of mature trees or landscape that could choke the sprinkler lines? Do all the heads have the same amount of low pressure or do some of the heads have better pressure then others?