I am glad to have found this place while searching for a solution to a perpetual problem I have been having.

It seems that at least three times a week I get p0172 and p0175 coing up simultaniously, which of course causes my check engine lite to come on along with restricted engine performance for a short time. It was diagnosed here in corn country as a bad maf sensor, which I replaced. After a couple weeks of driving the same conditions occur with both codes coming on at exactly the same time. I have monitored the car with my obdII scanner and has seen them display together. I am wondering if anyone may have some sort of idea as to what may cause this to occur. I lean toward the fuel pressure regulator but do not want to do anything without getting some feedback first...

Thanks to all that respond and I will be happy to assist others when I can

 

nooshin, those codes can also be caused by a crack in a vacuum line. I would be looking at your vacuum lines and seeing if any of them are in a condition that might justify replacement. Specifically, look at the lines running from the intake manifold over to the brake booster and the line running from the intake manifold to the PCV valve. Also, take a look at any hard line that is in these lines too. It is not uncommon for these lines to develop a crack in them (normally on the inside of the curve). After that, it will take a little bit of looking around. But, based on the year vehicle, I will be placing money that it is a vacuum line with a crack in it that is causing this.

 

thanks... I will check them and let everyone know what I find

 

I checked all vac-lines and all connections I could see, ran my hands along them etc... I believe that there are a few that could stand to be replaced, but none were cracked at this time. I do not have the correct fitting for my pressure guage to connect to the rail. What size fitting should I look for....
I should have indicated that the car has 69k miles...

after last start cycle, I found both exhausts to smell STRONGLY of sulfur and idle to be somewhat irratic, bouncing between 550 and 700 at idle speed
Thnks