Rough Idle and hesitaiting take off

subaru
rough
outback
hesitation

#1

I have a 2001 Subaru outback with 167,000 miles. Recently it has been running rough. I changed the fuel filter, changed the spark plugs and wires, changed the air filter, checked the vacuum which was normal and just changed the ignition coils. All this did was cure the misfire in cylinder 2. I can’t figure out why the car still idles rough at a light (usually)and most take offs have a hesitation. The car seems to run fine while traveling local roads and on the highway. Gas milage through this has not suffered. What gives with the family chariot?


#2

Throttle position sensor perhaps.


#3

Assuming you have had a computer scan for trouble codes and found nothing, I would take a cylinder compression test. Did this condition develop slowly or overnight? Did you have work done to the engine before experiencing the problem?


#4

Did you check the ohms or volts, of the throttle position sensor (tps), at idle and just off idle? If the ohms, or volts, don’t change smoothly, as you move the throttle off idle and back, the throttle position sensor is faulty, the engine performance will be erratic at idle, and just off idle, correspondingly.
You need to check the fuel pressure at different throttle positions. If fuel pressure is low (or, high) at idle, idle rpm can suffer.