1997 Plymouth Voyager wont accelerate

Recently while driving the van has stoped accelerating, it started doing it at about 60mph. Then the next day after driving for about an hour I came to a light and wouldnt accelerate above 25mph. I took it to 2 shops, one was usless, and the 2nd hooked it up to the diagnostic machine and couldnt find anything other than a problem with the vacuum hose. It drove fine the 1st day after wards but I just came back from a 15 min drive and not only did it stop accelerating, it also started to jerk and make a popping noise. It sounded like a bag of pop corn going off under the peddle and I could feel it at my feet. It wouldnt go more then 10 or 20mph. Please help no one seems to be able to tell me whats wrong.