Heat loss at idle on 2003 Mitsubishi Eclipse

Hello all, I am experiencing heat loss only at idle. Blows very warm (normal) on acceleration, but turns cool while at idle (stop light). Temp always sits at half, rad fan almost always on, no overheating. Would not think heater core, as heat is warm, no damp floor, or window fogging. Coolant full (not overfull). Vehicle is a convertible. Thanks all for any info.

Asked by for the 2003 Mitsubishi Eclipse
i would have the system leak checked in the cylinders. it is sounding like a head gasket issue. may have happened a while ago.

1 more answer
might also be a partialy clogged heater core ..acceleration makes more pressure therfor youll get heat at idle less pressure and no heat