Must have damaged a spark plug or mixed up the firing order during replacement. Check the code(s) and you may find a P0300 thru P0308 which will help determine what cylinder is misfiring.
The 2003 Toyota Sienna has a V6 engine.
The 2013 Toyota Sienna has a V6 engine.
The 2010 Toyota Sienna has a V6 engine.
The 2002 Toyota Sienna has a V6 engine.
The 2006 Toyota Sienna has a V6 engine.
The 2001 Toyota Sienna has a V6 engine.
The 2014 Toyota Sienna has a V6 engine.
The 2007 Toyota Sienna has a V6 engine.
The 2009 Toyota Sienna has a V6 engine.
The 2008 Toyota Sienna has a V6 engine.
The 2005 Toyota Sienna has a V6 engine.
The 2004 Toyota Sienna has a V6 engine.