The Subaru Outback uses the same reliable four or six cylinder opposed engine as its companion models. It is computer controlled and uses several sensors to communicate with the programmable control module. Diagnosing a low idle condition requires reading the data stored in the computer.
Getting information from the computer requires the use of an OBD-II scanner. While the dealers use expensive proprietary machines, inexpensive consumer-grade models are readily available at any auto parts store. The devices come with a book or website that will explain the trouble codes.
A leaking vacuum hose or fitting, a leaking EGR valve or clogged air filter can be a cause of poor idling. These issues are easily repaired with simple tools.
Low fuel pump pressure is considered serious because the pump replacement procedure is labor intensive. Leaking head gaskets, worn camshaft lobes and worn timing belts require expensive repair procedures and specialized equipment.
