There's a corruption problem, and the US will use it as an excuse to target politicians unfriendly to their interests, and divert scrutiny away from those that play ball with Washington.
Plus the few cases when US companies (or they local subsidiaries, more exactly) do get tangled up in a corruption thingie for one reason or another the companies themselves get out of it as nothing had happened.
Here's an article about a former CEO of Oracle Romania [1] recognising that he took 500,000+ euros as bribes, but because he reached a deal with the prosecutors he received a suspended sentence (so no actual prison time).
And, the most famous, the Microsoft scandal [2], which has its own dedicated wikipedia page, but where, again, the company itself got away without anyone working for them actually being prosecuted. I'll give it to the American authorities on this one, though, that scandal was most probably put into motion at the very beginning thanks to the work of the FBI [3] (so, obviously, as the result of domestic US investigations), the FBI which had also found irregularities with MS's work in China and Italy.
Is there a corruption problem in Romania, and the US is trying to help overturn it?
Is there no corruption problem in Romania, and the US is doing some power play to try to get the people in power out?