I had that same problem....... but mine was a fuel pump going bad...... when I was a 1/4 of a tank of less the car would hesitate at higher RPM's..... But no matter how much gas I had in the car the idle what jump by itself.... it would "hang" and then drop back to normal... I took out the fuel pump..." another bad design by FORD" and the screen for the pump on the bottom of the pump was sitting on the bottom of the gas tank.... I tried to put it back on it wouldn't go back on.... So, I bought a new pump and installed it and the hesitation went away... the throttle hang went away...
I figure the reason that the rpm's where reving up by themselves is that the computer was trying to compensate for the lack of fuel.... I took apart the pump and there was a lot of dirt and such in it... So, I guess the best way you can figure out your problem would be for you to get a fuel pressure check..... I don't see how jamming a copper pipe cap into a hose would fix the problem?????? I think it just masks the problem........ It may not be the fuel pump.... but maybe something else... anyway you loose power with that copper cap....
