More than likely it has to do with the charcoal canister which is part of the EGR (exhaust gas recirculation). The unburned fuel in the exhaust is routed to the canister where it is stored until it reaches a certain level. At that time a solenoid causes the gases to be purged from the canister...
It could be the fuel pump or timing belt. I hope it's not the timing belt, the fuel pump is bad enough. Not likely, but bad gas could also be the culprit.
Being that it is a twenty year old car, you're unlikely to find a suitable engine that would be worth buying. You just won't find one with low mileage and any other engine would likely by close to worn out. If it were me, I would be looking for a push, pull, or drag it in sale and trade it in...