When will it end, seriously
 

Is this normal for a car to replace part after part failing consecutively?

In the last two months I have changed the MAF, the purge valve and then the turbo control valve. Not to mention that I have serviced the PCV and et al.

Now, I have the CEL and it is saying front oxygen sensor.

Is this typical to have one part fail at a time and after replacing a new one?

And lastly, would a bad oxygen sensor cause a rough idle? Ughhahsfsja;fsajfls;af!

Are you just replacing parts because of CEL warnings? If so, if you just go by what the CEL is you might be replacing the wrong part and not getting to the source of the problem. A CEL for an O2 might be an O2, but it could also be something that is triggering the O2 to go out of range.

Well, when a CEL comes on and I get the code I go to this forum and assume that is the problem as thats why the CEL is coming on. I am not randomly guessing what could be the problem.

A CEL indicates a malfunction or a reading is out of range. It very well could be the part the CEL is indicating, or it could be something related (ie. O2 could be maybe a cat or a fuel injection issue, etc.). If you're just replacing what the CEL is throwing, you're not actively looking at addressing the problem.

Ok, fair enough
 

So, I have a really bad rough idle and the codes say O2 sensor. I also have poor fuel mileage and a firecracker smell.

What could it be then?

When accelerating it wont surge like some of the other throttle body problems and if I get on it, it will go.

So, if I cant rely on the codes how am I supposed to figure out whats wrong with it?

I will await your guidance. Thanks in advance.

welcome to the ART of auto diagnostic,
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$100/ hour volvo technician!

sounds like a possible vacuum leak