They were at warp. The wormhole instability happened after they achieved warp 1. It was the result of an instability in the warp field turning the warp bubble into a different, more dangerous and uncontrollable kind of faster-than-light spatial distortion, and it dissipated once the warp drive shut down.
http://www.chakoteya.net/movies/movie1.html
That makes it clear that they were above the speed of light during the wormhole event. Of course, a warp drive and a wormhole are variants of the same physics, both distorting spacetime in a way that effectively shortens the distance to a destination so that you get there faster than a beam of light in normal space -- the former by "surfing" on a distortion wave that compresses space in front of it, the latter by creating a "tunnel" through spacetime that's shorter on the inside than the outside. So the idea was that it was the imbalance in the warp field that distorted the spacetime metric from a warp bubble into a wormhole.
Note also that after they got out of the wormhole, Kirk ordered Ilia to "lay in a new heading" to intercept the intruder. That tells us that they'd moved significantly through space while they were in the wormhole, far enough that they needed to recalculate how to reach their target. That wouldn't be the case if they'd been slower than light. On the contrary, the wormhole probably sent them significantly further than warp drive could have in the same brief time -- but since it was unstable and uncontrolled, they had no way to predict where they'd come out. Or when, given that it distorted time as well.
It's pretty clear I meant going to warp without a problem. I shouldn't have to spell it out so exactly. But I forgot for a moment that I was posting on TrekBBS.
You know what? Forget it.