You arn't Mike's little bro are you? If so I have spent quite a bit of time workin on that rig, we've had it doin some sick stuff b4
Anyway, it could be a number of things, but its probably vacum related (at least i would start there), there are some dudes on here that are xj fuel injection experts, i'm sure they'll chime in.
if you don't have a haynes/chilton/etc type manual i would go snag you one from your local advance or autozone, it covers alot of the basics and has a troubleshooting guide that can sometimes help you diagnose problems such as the one your having.