Sounds like intake manifold gaskets.  If you had warranty work done on your
front timing chain tensioner, they should have been changed.  Usually its
the lower manifold gaskets that cause the problem, but in my case I had the
timing tensioner replaced at the dealer, ended up replacing the intake
manifold gaskets myself and upon reassembly discovered that the upper
manifold wasn't properly torque at the dealer.  Relatively easy replacement
job with manual for reference.  You could also check the Idle Air Control
(IAC) valve, clean it out along with the air passageways, but in all likely,
you have a gasket leak.