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Rich Rough idle help

982 views 7 replies 3 participants last post by  turbo_shelby 
#1 ·
So I got a rough idle today on my way to work. When I came home I checked all as lines and everything's looked good. I noticed that my o2 sensor connector was touching the manifold, yikes. Two wires had the insulation burned off and the bare wire was touching the manifold. I cleaned that up and did a continuity check from one side of the plug to the next. Everything checked out ok.

The cel never came on, but it threw only code 51 when I checked for codes.

I also get 20" hg vacuum at idle.

My Wideband reads around 12 at an idle whereas before it was 14.5ish.

Car run awesome except my wide and is reading rich at idle and cruising... Any suggestions?
 
#5 ·
A standard O2 reacts to oxygen content in the exhaust stream through a chemical reaction that produces a voltage, .1-.9 volts.
The lower the oxygen content the lower the voltage output.
The controller is always trying to maintain Stochiometric (14.7/1 AF Ratio) in closed loop.
Reading O2 voltage that would be .450 volts.
Voltage constantly crosses above and below .450 volts as the controller makes small fuel trim corrections and the O2 reacts to the ever changing oxygen content in the exhaust.
If voltage drops below .450 volts and controller fuel corrections cannot rectify the condition a Code 51(Lean Exhaust Indication)will be set.
Anything that can cause a lean condition or excess oxygen in the exhaust stream(exhaust leak, misfire) will cause a Code 51 to set.
Since you had an issue with your O2 sensor it is safe to say that is what is causing your problem.

The only difference bewteen an O2 Sensor and a Wideband A/F Ratio Sensor is the Wideband reads Air and Fuel, not just air.
 
#6 ·
For future reference if anyone searches for a solution.

My issue was a poor idle when warm. I also got poor fuel economy. The car ran without a hiccup at WOT. Cruising and idle my wideband read 11.5-12.5. I found that two wires on my oxygen sensor had touched the exhaust manifold and the insulation melted through. The wires could touch the manifold directly. (Ground path)

I replaced the oxygen sensor and the car idles normally and is back to 14.5-15 on the wideband. I also an getting better mpg.

Thanks NAJ.
 
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