Using variable valve timing, you can "backwash" intake valves during the compression stroke without an intake injector. Ford patented it almost 20 years ago.
A method for a vehicle traveling on the road having an engine with adjustable valve operation is described. The method includes performing a valve cleaning operation for reducing deposits on a valve of the engine; and at least during said operation, adjusting valve timing of at least a valve of...
patents.google.com
We have a 2013 CX-5 with the 2.0 skyactive without any engine buildup problems.