Upper and lower intake manifold seals leak on the 3.8 and cause a host
of problems. They are tempermental esp. in cold weather because they
shrink excessively and allow lots of unmetered air into the cylinders,
severly leaning out the engine at idle. You may experience drivability
concerns and/or a check engine light (codes P0171 and P0174, banks 1
and 2 lean).
Also, your mass airflow sensor could have dirt built up on its hotwire.
This is another common leaning condition; but is less temperature
sensitive than leaking intake seals.
The upper intake seals are fairly easy to change. There are "seal
washers" under the holddown bolts that should be replaced also to
improve clamping force. There should be a Ford TSB on this.
Toyota MDT in MO