P0171 & P0174

[PAUL T]

My wife called me last night and said the CES light came on in her 97 Deville and codes P0171 & P0174 were current. I know Logan explained that a cracked plenum will cause this. Is there anything else I shoud inspect that may also cause this situation? Maybe other vacuum connections? Should I just go ahead and replace my plenum? I plan on looking at it tonight, so let me know your opinions.

PAUL T.

[Ranger]

Paul,

There is no "plenum" on your engine. The "plenum" is the rubber coupler between the TB and the manifold on the 2000+ Northstars. Look for a vacuum leak elsewhere.

[PAUL T]

I was thinking maybe there was not a plenum. I quickly checked the vacuum lines last night and did not find any problems. The problem seems to be intermittent though because when I drove it yesterday the codes were history. I can drive that car for 2 months without a problem but let my wife drive it and something alway happens. Maybe a woman thing? I drive it like I stole it and she babies it, that is probably the problem. I am driving it today so I will clean her out.

[BodybyFisher]

The problem is that whatever is wrong has to affect both banks creating a lean mixture due to unmetered air. That is what drove you to the plenum, and its the first thing that I would have thought about.

If your throttle body is bolted to your intake as mine is, check the gasket between the throttle body and intake and check the tightness of the throttle body fasteners