I have had a Code P1131 Come and go as it pleases. 98 4.6L It started right after I changed the Plugs and Wires at 112,000 miles. I'll get a rough idle and then the check engine light comes on. If I wait through a few drive cycles it will go off. All the vacmun hoses are good, The PDFE Switch and EGR Valve are new.

P1131 = Instff. Control Valve Switching / Lean

Any Ideas?

 

P1131=Lack Of Upstream Heated Oxygen Sensors (HO2S 11) Switch, Sensor Indicates Lean (Bank #1).

This is the oxygen sensor on the passenger side exhaust manifold indicating that side of the engine is running lean (Too much air, not enough fuel). This is most likely telling you that there is a vacuum leak on the passenger side of the engine.

You'll want to check the PCV valve to make sure is is pressed in securely and that the hose itself is not cracked. A cracked hose is actually failry common on a 4.6L engine.

If you can't find any leaks, switch the driver side HO2 sensor with the passenger side and see if you then get a code for the driver side of the engine. If the code follows the sensor to the driver side, the sensor is bad. If the code stays on the passenger side, the sensor is good and you have a vacuum leak or fuel flow problem.

 

Thanks it sounds like good advice. I checked, replaced and clamped all the vacumn lines. The PCV hose is hard plastic except for the connecting ends which are also clamped. The PVC is also seated well. I did not think of switching the sensors. I'll try that next. What is this rubber hose on the back of the engine and where about on the back of the engine? 98 F150 4.6L

 

i had the same exact problem, never found a leak. i changed the upsteam O2 sensor on bank1(Passenger side), and have had no more problems. go to napa or autozone, they have them for $50. ford wants $150 for them. you'll problems will go away. oh yeah, get a 7/8 inch opened ended wrench to get the O2 sensor out. don't worry about that special socket they make for it. the 7/8" will do the jobe just fine.