I'm hoping someone can give me some insight with this problem. I'm getting 171 and 174 codes on my Exp. I could not find a vacuum leak ( at least not yet ). Having both codes makes me think whatever is causing the engine to run lean is common to both banks. I'm thinking that it eliminates both upstream O2 sensors, as it's probably very unlikely they would both fail at the same time. There is a new air filter. When the engine is cold it runs fine. When it warms up, it runs rough at idle (approx. 450-500 rpm). There is no noticible problem during acceleration or when driving, just at idle, especially when in drive. Any ideas? I would appreciate any help I can get. Thanks.

 

Clean your MAF with electric connector cleaner. Had the exact same codes and couldn't find a vacuum leak. ( Behind the throttle body is the PCV hose and usually the elbow in the line cracks )

Haven't seen SES light since cleaning the MAF.

 

Dont know if this will work in your particular case but here goes...Same two codes popped up on my 97 Expy 4.6 with 149k. After scratching my head for about 3 weeks checked pcv on passenger side...followed the line around back of intake and took it off. Much to my surprise the line was a "hard" line that was actually molded plastic with two lines which looked like fuel line hose. Replaced two 2 inch pieces on each end of the line and reinstalled. 1 week later...codes have yet to pop back up. Codes were coming on daily.

Hope this helps before you go and spend a ton of money.

 

Thanks, that's what I also found and now all seems well.