check for vacuum leaks, and also for any SLIGHT gasoline leaks that might possibly be occuring before it arrives at the intake manifold. umm..lets see, what else might it be.. OH check sensors, you might have a faulty 02 sensor or something thats registering your exhaust gases wrong (saying they're too lean), or not at all, and so the computer's trying to fix it by dumping fuel into the cylinders. In other words try the basics first..it might be a cheap fix, no use getting worked up and throwing all kinda money at something that might not even be the problem, especially when there's simpler, cheaper things to try first.