Hard idling I have a 2003 VW Passat 1.8T. I talked to a mechanic about the rough idle and he told me a couple of possible causes. The first i do not remember.... LOL..... only that it had something to do with maybe a regulator of some kind, located on the engine manifold. The second fix was to remove and either replace the mass air flow sensor or clean it. I was changing the air filter the other day and found the mass air flow sensor, but could not access it easily do to another tube running out of the front of the air box that I couldn't remove because of crimped hose clamp. The hose was made partially from molded plastic and was oddly shaped. It turned 90 degrees straight down. My first question is, does anyone know what the device on the engine manifold is and what I'm suppossed to do with it? Second, are there any other probable causes for the rough idling? Third, what is the hose and where is it running to below the air box?