Mnsubaru

I ran the codes and the first code was for the O2 sensor and the second code was for #2 fuel injector and that was all i got that time. Then I went back about an hour later and ran it again to double check and I got a third code I believe that was for the speed sensor or something. A buddy told me that if the O2 is bad that it will give a injector reading as well at times. My first question is how many O2 sensors are on here it should just be the one in the exhaust by the y pipe kind of right?? the book seemed so say there was a couple of them but i've got a hayes manual that covers several years etc. My second question is how hard is it to replace and is 93 dollars a good price on an O2 sensor also would a junkyard part work let me know thanks alot guys this site is great.....

Hello i'm new to the board and it seems great. I've got a 90 legacy and it started running really wierd yesterday it started running like a diesel and has no power runs rough real rough and like I say no power the "check engine" light is on. Now it ran like that for 50 miles then just up and quit, I shut the car off and went in for a bite and came out and ran perfect for another 50 miles then parked it and re started and it runs terrible again i'm just curious if you think it is the throttle positioning sensor or the EGR valve or what. I'm assuming that if the check engine light is on its something to do with the emissions or a sensor I could be wrong but thats my guess hope to hear back and thanks in advance.. P.S. it does idle but barely