All the voting intention polls since the 2005 elections. The vertical lines are the election dates (2005, 2009, and 2011), the lines in color are lowess smoothers (25% bandwitdth). Data taken from here and here (and from my own data until 2009).
On the coalition parties, the PSD is at its lowest level since mid-2010, and the CDS-PP has also been also dropping since the 2011 election. But note how the CDS-PP rose as the 2009 and 2011 elections approached. Predictably, the CDU (the Communist+Green coalition) is the most stable party. Consider, however, that almost all polls since the 2011 election have come from only three polling institutes: the Catholic University has published only two polls since that election and Intercampus hasn't publicly polled since June 2011.