Lean code P0171
FTE Legend
Joined: Jun 2006
Posts: 31,930
Likes: 1,499
From: Ottawa, Ontario
It's probably not the O2 sensor, look for a vacuum or exhaust leak first, or a gasket leak at the intake. Use an unlit propane torch to spray gas around possible leak sites, if the motor idles up you found the problem. The other possible cause is a dirty or malfunctioning injector.
Elder User
Joined: Jan 2008
Posts: 605
Likes: 1
If you have a scan tool you can monitor the STFTs. That's the way to go. Watching the STFTs is more sensitive than trying to listen for the idle speed to change and the STFTs react very quickly. You really need an assistant to do this properly. One to spray and one to watch the STFTs on the scan tool. You want to note the exact moment the STFTs GO RICH since you are currently LEAN. This is the area where you will look for a fault. You can also monitor the RPM on your scan tool if you want at the same time you watch the STFTs. You can use propane or a solvent in a spray bottle or aerosol can. You might want to put a piece of cardboard between the fan and block. The air from the fan plays hell when your trying to spray something in a certain spot. Steve deserves credit for the STFT idea.
