Hi Christine,
Sounds like your car has a running rich problem. Cold starts after sitting for hours are better because a cold start needs more fuel. I'd be interested to know how "well" it is really running after warming up. There are several things that can cause rich conditions (mine, a 1990, turned out to be the ECU). After the car is really warmed up take note of the idle at stoplights. Is it stumbling? Any smoke in the rear view mirror? Take it out on the highway and step on it and see if the downshift is accompanied by black smoke. If so, the car is running rich all the time (as mine was). If you don't observe the above it's probably linked to one of the temperature sensors (air box, ECT). You might also check the fuel pressure regulator or the vacuum hose connected to it. If the diaphram inside the FPR is bad it won't return fuel to the tank properly (and will leak gas back through the vacuum line connected to the intake...contributing to high fuel pressure and additional fuel routine back through the vacuum line). Continue observing the car's behavior at all times and start ruling out the cheap things first. The FAQ page has a lot of good info on rich running, etc. Jon