1990 Corolla, trouble starting

Hey guys, I own a 1990 Geo Prizm/Corolla. It has nearly 200K on it and so far this has been a perfect little car (ie, no major problems and I only have to perform routine maintenance). Within the last month, it has had trouble starting. The exact problem is this:

When my car has been sitting for hours and I go to start it (usually before and after work), it struggles to start. It cranks right away, but it will not turn over unless I press down the accelerator and give it about 10 secs. of gas. Once it turns over, it runs fine. If I stop the car to do errands or stuff, the car will start just fine when I return. The problem only occurs when the car has been sitting for many hours.

I believe the problem to be the fuel pressure regulator and/or the fuel pump, but both these parts are expensive and I’d like to rule out any other cause before I buy them.
As background info, I have replaced the battery, fuel filter, spark plugs, wires, and ignition rotor all within the last two months, so none of these can be causing the problem.

Has anybody seen this problem before and know what is causing it for sure?
Any suggestions?

Alot of mazda 3's had the same problem you're talking about. If I had to guess without taking fuel hold pressure readings, I'd say it's gonna be your fuel pump. When a car is parked overnite, a certain amount of fuel is supposed to be held in the line by your fuel pump. (Or a check valve therein)
Your pump isn't doing that, and therefor, you're having to rebuild the pressure all over again in the mornings. It must be holding for a little while, which is why you can go in the store and come back out with no problems.
(It's fairly common for this to be the case.)

To contrary, holding the accelrator down actually shuts fuel supply off (on EFI). I'm assumginthis is throrrle body injected? Could still be the pressure regulator or injectors leaking.

Another thought is engine timing?