It's behind the throttle body. You can see a rubber tube coming out of the top of it. It looks like it's hard to change. You find it easier to get at if you remove the black wiper cowl.
BTW mine was just changed at almost 60,000 miles, and it made little difference. If it's not sticking, it can last and last. After you replace it, check the old one to see if it's still rattling--or if it's on a spring, to see if it's not sticking. if not, you should save it.
2005 Dodge Grand Caravan SXT, 129K mi.
Former owner of:
1988 Dodge Caravan SE, 2.5L I4 (1988-1995, 99K mi); 1995 Plymouth Grand Voyager SE "Rallye", 3.3L (1995-2004, 169K mi); 2003 Grand Caravan Sport, 3.8L, (2004-2008, 106K mi), 2008 Nissan Quest, (2008-2010, 25K mi)
2008 Lexus RX400h (Dark Gray), 112K mi; 2005 Hyundai Elantra GT (Blue), 89K mi