Subaru Problems? Ask a Mechanic for Answers ASAP
Hello and welcome to just answer and allowing me to assist you.I may need to ask questions to get a better picture to help.When you replace or disconnect a battery the ECU goes through a time of relearning all the inputs and driving habits to control the engine managements. Also in some cases if it does not correct itself the throttle body builds up deposits that need to be cleaned .This can be done using a proper throttle body cleaner sprayed into the opening using a tooth brush cleaning it while holding the throttle plate open.. use a light to see inside to make sure it's all clean. https://www.youtube.com/watch?v=41yFXjibtLY
If that is the issue after driving a coupls times it should, but like I said if it don't then next step is to clean the throttle body as in the video I sent, varnish restricts the plate from returning to original position and the ECU does not recognize this.