Toyota Repair: 2000 Toyota Corolla, toyota corolla, delivery problem

Question
I bought my car new, it had only 18 miles used.  Within 2 weeks of purchasing my car it started to hesitate.  I give it gas and it acts like it wants to shut off.  I of course took it to the dealer...lets just 8 trips later, one engine replaced (it blew before the warranty ran out) several trips to other dealers, they could never find out the problem..when they would work on it the problem would disappear for several weeks and then reappear.  the car is now 7 years old and the problem is getting worse.  the car will shut off when driving.  When stopped I have to keep my foot on the break and the gas at the same time just so that when i take off the car will not stall out.  This car has been to toyota mechanics in alabama and georgia, plus some private mechanics...if you could possibly tell me some of the things that it could be, i have another mechanic that is going to take a look at it later this week and maybe this would help him.

Answer
With all of this going on there should be a check engine light that also keeps coming on when this problem happens, the only thing I can think of that may cause a problem like this is a fuel delivery problem which may not trigger the check engine light, has anyone ever checked the fuel pressure and made sure there is not a problem with the fuel pump?