Tightened bolts on valve cover then check engine light came on..?

[kahl]

High chance your heater core is leaking. Some great vidieos on how to change out core. Not a hard job.

[bmdubya1198]

+1, gotta be your heater core. Do you smell antifreeze?

[scot850]

OP mentioned he is NOT losing water (I'm assuming coolant).

Gin, when you say the floor is wet, is it all of the floor, the front mainly, the RH front, LH front, the rear?

If you are 100% you are not losing coolant, then it is not your heater core. When the heater core starts to fail, you get a sickly sweet smell, often accompanied by a greasy feeling to the inside of the windshield. The carpet is usually much wetter under the carpet than above. Please check.

Do you have a sunroof (moonroof) in your car?

The area you are getting the wetness on the floor is important.

If you can give us some more accurate details, it may help us to give suggestions where and what to check for.

Neil.