Yes I have, and a day later it will give you the dreded PO0420 code for the converter to be replaced, but it will give you the same code if you have a vac leak........ with the car off, go under the hood and locate the fuse block and pull the ecm fuse and replace a minute later and all is well again Been there, done that!!!!!!!Just to confirm: You're running two full cans of 'foam into ONE tank of gas? I just bought a used '01 V w/215k and my mileage is a piss poor 15.5. Just had timing belt and water pump done as well as a new air filter so I'm monitoring to see if that helped but I also plan on hitting it w/Seafoam (added to the fuel tank) this weekend.
Also: Ever done it through the brake booster/throttle body? I've seen it on YouTube and read about it on a DIY site. Also I believe that's what the directions on the can say to do.