P0172 and P0175 codes

My wife's 2000 Windstar with about 92K miles had a CEL that the code reader showed as P0172 and P0175 (banks 1 and 2 rich), with no other codes. I reset the codes and the CEL didn't return for a little over a week. I saw several posts that suggested that the O2 sensors or IMRC could be the cause, but in all of the posts I've seen, there has always been some associated code. Does anyone have any ideas on this one?

BTW, this vehicle has had numerous CEL for lean codes in the past; replaced the MAF (twice) and followed a TSB related to a leak in the intake. All out of warrantee (of course).

Thanks

I recently had the P0172 and it was associated with another code. However, from my limited experience the only time I've had this code it has been tied to the IMRC and a vacuum leak of some sort was the cause.

Prior to the most recent one, I found a bad PCV hose that had a hole in it. The first time I had the codes read Autozone tried to sell me 4 o2 sensors. After reading the forum I was convinced that the o2 sensors rarely fail but are often sold as the fix because of the definition of the code.

I'm new to this, so if I'm off base here someone jump in!

Either a vacuum leak, a bad PCV hose, or an intake leak will cause those codes. Replacing the O2 sensors will not fix it.

Possibly a bad fuel pressure regulator.

For the fuel pressure regulator, part of the TSB for the upper intake manifold bolt isolators has to do with the vaccum line going to the fuel pressure regulator. If that is acting up, causing a vaccum leak, that can be your vaccum leak.
The other part of the fuel pressure regulator vaccum line is the fact that the regulator REDUCES the fuel pressure as the vaccum increases (which happens under lighter engine loads), so a vaccum leak in the line can cause lower vaccum to the regulator, resulting in higher fuel pressure to the fuel rail (and thus the injectors) than what is intended.

OK, thanks. I'll check that out and let you know what I find.