Need some help with SES codes...

OK, my 2003 GT started throwing a SES light at me the other day. Pulled the codes and got four things-both downstream O2 sensors and P0171 ans P0174 both banks running lean. I checked out the O2's and did end up replacing them, one was definitely shot so I just swapped them both. Reset, and still getting the P0171/P0174. After doing some digging on this forum, I see that this is most likely a vacuum leak, problem is I do not see anything wrong with any of my vacuum lines. Motor is stock and has not had anything removed from it recently that would cause this issue. Is there any likely place that tends to cause this issue, or could this vacuum leak be basically anywhere? Also, is there an easier way to tell where the leak is? A visual inspection turns up nothing, I removed, checked, and then put back on every vacuum line I could get my hands on, with no luck. Removed and reinstalled my air filter/intake tube just to check, no difference there either. Any thoughts?

Thanks for the ideas!

I should have mentioned, I pulled the MAF and cleaned it earlier tonight, no change. The car drives pretty much normally, except it drinks noticeably more gas now. At idle, it is normally right about 600-700 rpm and smooth all day long....and now, since this started, it is rough and the rpm bounces a lot. I also noticed that when I stop at a light, the rpms stick around 1500 or so, instead of coming down to normal idle right away. After a few seconds, it will then drop down.

I dont have a code reader for OBDII, mine's an OBDI for use on my other toy--1995 Thunderbird SC. But I have a friend at a local shop and I used their scanner earlier. I am going to give the carb cleaner a shot tomorrow and see what I find. A vacuum leak is actually probable, since when I had the hood up today I heard a noticeable hissing sound while the engine was running. I know this engine sounds a bit like that anyways, but it did sound louder than normal. I'll post back what I find tomorrow, thanks!

Jon

Thanks for all the replies! I found the vacuum leak, I probably overlooked it the first time because it was so small. So, a new section of hose went on, and the computer reset....and it idles and runs just fine. I will definitely look into that code scanner too, thanks for that tip also! The Mustang is actually for sale now, only because I need a new work truck and I already have three Fords plus my wife's Ford Freestyle. It was either sell the Mustang, or sell the Thunderbird, and they only made 574 of this T-Bird in 1995, so the GT has to go, I guess. Hate to get rid of it though, its been one of the most trouble-free cars I have ever owned. This vacuum leak is the biggest problem I have ever had with the car. Aside from that, its been regular maintenance and new tires, thats it!

Anyways thanks again! And if anyone knows of someone looking for a very nice 2003 silver GT, shoot em my way. Selling it well below book value because I already have a truck picked out and need to get this car out of the driveway and off the insurance first....