Shot in the dark...
...but, are you loosing any coolant? The symptoms you are describing are similar to those I experienced when my head gasket was beginning to fail.
'04 ML500 - 53k, Inspiration Edition, Desert Silver
'11 Audi A4 Avant - Brilliant Black
'87 300SDL sold
'99 C280 Sport sold
'85 190E 2.3 sold