Chevrolet: chevy venture idle problems, intake manifold gasket, vacuum hoses

Question
I have a 2001 Chevy Venture with a 3.4L fuel injected engine.  I started out repairing a coolant leak from the lower intake manifold gasket.  The van was running fine prior to starting the repair, except for the leaking coolant.  After completing the repair job, the engine no longer idles well.  It seems to run ok at higher rpms.  There's more to it, though.  When starting a cold engine, it starts and idles ok.  As it warms up, the idle gets worse (maybe when it goes into closed loop?).  I get no trouble codes, except 0171 (system too lean) on occasion, but not right away.  I tested the vacuum with a vacuum gauge and am getting around 16-17in when its idling good, then it fluctuates around 4in when it starts to lope.  I've inspected the vacuum hoses and they appear to be ok.  Here's the last piece of the puzzle - which may or may not be relevant, but at this point I'm second guessing everything.  I noticed that the water coming out of the exhaust is accompanied by black stuff, I'm guessing carbon, that floats on top of the water.  It's not smoking, however.  When I had the intake manifolds off, I cleaned them (inside and out) with an engine degreaser.  I'm a little scared that that was a bad idea and it left a residue that is burning off when the engine warms up, and that is causing my idle problems.  Any thoughts you have would be appreciated.  Is the "black" exhaust liquid normal/unrelated?  Thank you.

Answer
Trav;
 As far as the water if it is not that much , like drops that go away after it is warm than it is moisture but if it is all the time , there could be a leak or bad gasket or re-tighten them, also was the distributor removed ? if yes that could be whats wrong .. the engine de-greaser is fine it hutrs nothing in that area.