Okay, i'm a newbie and i have only been driving my volvo for a year or so. I don't really know much about anything really. I was stopped at a light a while back and my car suddenly got really loud. I get it home and find out that the oxygen sensor has fallen out. I try to stick it back in and i find that the threads are completely chewed up, unfixable... so to speak. I took it to a local volvo specialist, and they charged me 145 bucks just to look at it and tell me it was going to cost me an additional 300-400 bucks to have them fix it. I know when im being taken advantage of, and this guy was tryin to screw me. My point is, i know i shouldn't try to drive the car like it is, and i don't have much money. So i bought a used manifold off of a dealer, and decided to do it myself. I don't really know how to do this, and the chilton repair manual doesn't help me much. I know i need new gaskets, and not too much else. I need any help i can get, my knowledge is limited. Thanks for helping and sorry the post is so long. Jason

Buy a can of P'blaster or other similar rust loosening type solvent. The studs on the exhaust manifold will be very rusty, so more than likely the stud will turn with the nut if you try to remove them. A repair shop would be wise to use a torch to remove the nuts (not to cut them off, just to heat them, then loosen).

You need new gaskets between the head and manifold, and a new metal gasket between the manifold and the y-pipe. Soak those bolts too before trying to seperate the manifold from the exhaust.

It's a dirty job, and could become problematic if you snap a stud flush with, or inside the head. But it's relatively simple in nature. The O2 sensor is 22mm or 7/8" (either will work). I'd recommend buying an O2 sensor socket, as they're easier to use in tight spaces than a long wrench.

Are the threads on the manifold chewed up too, or just the O2 sensor? Dumb question perhaps, but a new O2 sensor might be a cheap fix if the manifold is OK. Get a flashlight and a mirror to check the hole in the manifold (there's a mirror mounted on the inside of the glovebox door, which I use all the time for things like this).
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Yea, the threads in the back of the manifold are almost non existent, i too looked with a mirror, and its nasty. I don't have much tools, but i do have the o2 sensor socket, made just for that purpose. Its pretty cold here and i don't have a garage or any heated place to do this. Should i wait? I have been putting it off for awhile now, but its getting bad. I don't want to cause more problems by doing it myself, like i said, im a newbie.

spray the P'blaster generously and let soak overnight. try loosening nuts on exhaust manifold and downpipe very carefully. if you have any fear of breaking the studs on the head, just leave it to a professional. if you have a torch, i would try that too, as stated by michae1. good luck. another possibility is epoxy or that steel-like epoxy to seal the o2 sensor in. there are some kinds that will hold up to the heat of the exhaust gas, but im not sure which.