What makes car stall sometimes?

I have a 1994 toyota camry 4 cyl.The problem is once in a while it will stall.It Stalls mostly when im stopped in drive.if I try 2 press the gas it starts to make it stall worse.If I let go of the gas and press it again it will stop the stalling...(Sometimes That Has Not Worked).If Its Starting To Stall I Can Put it in park or nuetral and it will stop the it from wanting to shut off.If I let it sit when it wants to stall in drive it will fight to stay running for like 2 or 3 mins before it stalls.I replaced fuel filter,spark pulgs,tps and I added fuel system cleaner.when it does die I can start it up no problem.but sometimes as soon as I put it back into gear again it stalls.it did stall sometimes while driving.now this thing will work great one minet or for hours then bam out of nowhere it will happen.Then after a while it will be fine again.Very stressed out about this. Any help PLZ WILL BE APPRECIATED Thank You