Help w/O2 sensor

2001 2500hd 6.0 How do I know if my O2 sensor is bad? Here's what happened: I took my truck to the dealer cause it would sometimes idle rough and when it started to idle like that the only way to clear it up was to shut it off and restart it. So the dealer cant find anything except for a bad cat, so they replace it,truck runs good for about a day and then starts doing the same thing. So, i'm pretty sure it's the O2 sensor but how can I be certain? Is there a way to check them? Oh yaeh it's been on 2 different comps and shows no codes..And I've already done the fuel filter and the fuel pump has been replaced as well,along with the fuel reg.

O2 sensor should not be stalling your truck or roughning idle. and it'll throw CE light on. O2 sensor is part of emissions system, has little to do with driveability.
locate your EGR valve, pull it off and clean with carb cleaner.
run can of seafoam through tankful.
otherwise, there are many parts in this truck that can give you rough idle. but it all goes down to several things: bad fuel supply, bad spark, bad air supply, bad timing, air leak, coolant leak into the combustion chamber or cylinder. or combination of those. or all of the above.
hey, pull plugs out and check for contamination. also, spray soapy water on plug wires, if it starts krinkling - bad wire it is.

[quote=ukrkoz]O2 sensor should not be stalling your truck or roughning idle. and it'll throw CE light on. O2 sensor is part of emissions system, has little to do with driveability.
locate your EGR valve, pull it off and clean with carb cleaner.
run can of seafoam through tankful.
otherwise, there are many parts in this truck that can give you rough idle. but it all goes down to several things: bad fuel supply, bad spark, bad air supply, bad timing, air leak, coolant leak into the combustion chamber or cylinder. or combination of those. or all of the above.
hey, pull plugs out and check for contamination. also, spray soapy water on plug wires, if it starts krinkling - bad wire it is.[/quote
I'll try cleaning the egr..What would make a cat fail? and when the truck starts to idle rough and I try to drive it I cant get it over 20mph it never stalls just idles rough like a bad misfire. But I can shut the truck off and then restart and its fine and I might not have the problem for a couple of days or even weeks. I'm at a loss!!!

hey, pull plugs out and check for contamination. also, spray soapy water on plug wires, if it starts krinkling - bad wire it is.[/QUOTE]


What do you mean by "krinkling"?? Should you spray it with the engine running or off?? Just asking......I am trying to get a visual.

He means sparking or arcing from the plug wires to the engine block.

A friend just changed plugs on his Impala. after a week; he couldn't get the truck over 55mph no matter what he did. Turns out one of the new wires was touching the block; and was grounding out. Same symptoms of rough idle and low speeds only.

I agree the O2 will likely not give you a driveabilty problem especially without flagging a code.

These types of intakes are prone to vacuum leaks which can cause a ruff idle especially as the temps start to cool in the fall. When its acting up you can carefully spray carb spray around the intake manifold. If the RPMS change consistantly with a particular spot you sprayed than chances are its leaking. I have had them set lean codes for both banks and I have had them not flag any codes.