1998 Subaru Legacy

Engine Performance problem
1998 Subaru Legacy 4 cyl All Wheel Drive Manual

Hi, I have a 1998 subaru legacy wagon with 175k. Yesterday while passing a car the check engine light came on and it started running rough and now ticks. I had auto zone check it with their machine, it said misfire in all 4 cylinders. They recomended new plugs and wires, I did that and it runs better but still rough. I checked firing by removing wires with engine at idle and #2 seems to be where the problem is, no change with or without wire. What now? And what else should I replace at 175k?
October 1, 2010.

Engine running rough or misfiring can be cause by the following: 1. Defective spark plug
2. Inadequate spark/coil, defective spark plug wire.
3. Lack of compression
4. False air leakage.
5. Faulty fuel injectors.
6. Insufficient fuel pressure.
7. Contaminated fuel.
8. EGR valve that is leaking.
9. Oxygen sensors.
10. Throttle position sensor.
11. Idle air control valve.

Oct 1, 2010.