Just saw this post and you may have fixed it but my 1991 300 ec coupe did same thing. After many repairs over the years it turn out to be a sensor that talks to the fuel injection system & the elec fan system. Its a 4 prong sensor called water temperature sensor . It sends bad info to fuel injection system which causes too much fuel to engine which makes it act like it is getting flooded. As you speed up this fuel gets handled...Hope that helps.

My coup has several water temp sensors, so look fot the one with 4 prongs.