1999 Jetta GLS 2.0 AEG Fuel system problem

Hi, I'm helping a friend out with a 1999 Jetta GLS 2.0 AEG with what seems to be a fuel system problem. The car starts and ideals fine. Put push down on the accelerator and it seems to be starving for fuel. If the return hose at the fuel regulator is clamped, then it runs fine and the PSI on the inlet goes up. The filter has been changed making no difference in the problem and the voltage at the gas pump is 12.7-13.
Thanks for any help that is given.
Bill

Check all vacuum hoses for leaks/deterioration. Next scan the computer for codes. How many miles on the Jetta and what maintenance has been performed to date?
Franco

Thanks for your reply Franco. He check the vacuum lines and they seem to be fine. I don't have the mileage or know the maintenance info.
Do you have any other ideas?
Bill

I'm leaning towards clogged injector. A VAG-COM computer scan would find the cause. Without me their with the car is hard to tell exactly.
Franco