Recently my 2013 crosstrek started idling rough at stop lights.Sometimes it runs fine and other times it struggles with power . I had the spark plugs and serpentine belt changed recently but that didn't fix it.
Are there any Diagnostic Trouble Codes stored in the Engine Control Unit?
According to the service manual for the 2014 Crosstrek, top causes of rough idling are (1) a loosened or cracked intake duct, (2) a loosened or cracked PCV hose, (3) a loosened or cracked vacuum hose, (4) incorrect valve timing, and (5) an evaporative emission control system malfunction. Items (1), (2), (4), and (5) are also top causes of low output, hesitation and poor acceleration.
There are about a dozen other items that sometimes cause rough idling.