02 lincoln navigator idles wildly

My 02navigator does not idle right when in park or sitting at stoplight. I’ve gotten codes po171 and po174. The truck ran fine for a good 3 months after the (sevice engine soon light) came on and I got these codes so i decided to do nothing… Now it idles bad and has even shut off twice on me while pulling into driveway. I changed the MAF and that did nothing… Should I assume its the o2 sensors or is there a chance my CAT is shot. I’ve heard horror stories of guys taken cars into shop with same codes and the shop only correcting the problem after they replaced a bunch of stuff they didn’t need to…any help on this would be appreciated.

just googled the po171 code it said bank 1 running lean and 174 is bank 2 lean. it also said this might be a low fuel pressure problem so i ask you when was the last time you changed the fuel filter. that is where i would begain. if no difference have the fuel pressure tested.

It also be some sort of vacuum leak.

Get a can of starter fluid and carefully spritz around rubber vacuum hoses and assemblies. If the idle briefly changes and stabilizes, you’ve found the general area of the problem. The hose may have a crack or may not be snugged up properly.