Doesn’t sound like a valve problem to me. If its not a loose injector fuel line then it sounds like one of the injectors for what ever reason (crud got in the injector from the install) is not doing its thing. The way to tell which one it is; with the engine at idle wrap a rag (it’s going to get soaked) around the fuel line at the injector so you don't get soaked and loosen each line one at a time until you find one that doesn’t change the way it runs. Don’t take the line off just loosen it enough so the injector doesn’t have enough pressure to pop off (it won’t take much). When you do this it should make the engine run rough and lower rpm. When you find one that doesn’t change the way it runs or changes it just a little that is the one that needs attention.
Caution: the fuel is at very high pressure, be safe.
Hope this helps.