02 sensor

i have a question, what would be the symptoms of a bad 02 sensor? theres no check engine light on.. runs kinda rough when cold.. the air-fuel gauge works then doesnt work until i rev it high.. and all the connections are good.. would that be a bad 02 sensor? cause ive been reading and everone says they had a bad idle to almost dieing and they said they replaced the 02 sensor and it fixed it.. and when i unplug the 02 sensor it runs the same can u tel me if it is the sensor or not? thnx

I got a cel when my o2 went out. You may be pulling to much power from the sensor with that gauge and its not letting the ECU get the signal. Does the car drive fine?

Vacuum leaks can also do you in, but like Silver said the 2G will throw the CEL. When's the last time you had a tune-up?

i just put brand new NGK plugs and new wires in it like a week ago.. when i first got the car the air-fuel gauge was not hooked up and it ran the exact same.. the kid who i got it from told me that there is no egr valve and no "balance shaft" and he said that might be causing a rough idle. but when i start the car when its cold it almost wants to die.. i have to hold the idle up at like a grand or so until it warms up and then it kinda runs rough idles back and forth from a grand to 800 or so... and the BOV is recirculated and everything is stock.. if u need any more info let me know.

also the car drives fine.. i took it out after it was warmed up and it drives fine.. boost is good fine driving.. but its just the idle is rough and its annoying lol.. i just wanna fix the rough idle b4 i get my license back so i can do other mods without worying if its gunna run lik eshit..

Don't know man, I dont have any more input.

The o2 sensor shouldn't have much to do with the idle. When I first got my wideband, I took out the o2 sensor completely. I ran rich as hell, prematurely fouled out the plugs, and got about 120 miles to a tank. But my idle always stayed the same and was never choppy. Once I finally switched out cams, I get a messed up idle. But when i finally get the eprom and chip with the idle set to 1k i should be good to go. I'm not exactly sure what to say in your case with the car being all stock. It could be the EGR but I don't know. I had one case with a chevy blazer that had a piece of carbon stuck in the EGR valve causing it to stay open all the time. It ran at high idle, but it wasn't rough.

Yea that deffinately doesn't sound like the o2 sensor. Maybe check the idle control sensor on the TB or for vac. leaks.

alright thnx.. im gunna look around for any missing hoses or vacuum leaks.. cause i think theres a hose that was cut because the egr was akin out and shit.. so im gunna try plugging those up then ill let u know.. but my next deal is would it be worth it to buy a aftermarket header? cause if not then i dont wanna waste 300 bucks u know what i mean?.. but other then that im pretty much set for now.. thnx alot.

If its on a turbo car, then no dont get it. You would see very little gain, a stock manifold will do just fine.

If its on a nt car then it would be a good idea but 300 sounds high.

yes, its the 2.0 turbo

Port the stock manifold and it will flow plenty

Better yet, just get a 2g manifold.

Sounds like a not dead yet but dying O2 sensor to me. Having an innaccurate sensor is completely different from having no O2 sensor at all! With no sensor, it runs in open loop, overly rich, as people have observed. With a bad O2 sensor that the ECU s still trying to use, you'll get wacky AFRs.

Here's a current case. The EVO has a dying front O2 sensor a we speak. Uncounted gallons of 117 octane fuel have taken their toll on it. It still "works," but it cycles slowly at idle and at a lower voltage, doesn't come up to full voltage at WOT at 11:1, and doesn't like to start working until the engine is warmed up and at cruising speeds.

On a cold idle, AFR is 16-17 to 1, which provides a rough idle naturally. Occassionally it will go into the low 20s, where it often will stall or try to stall. One it's warmed up, it idles at 15:1, which works for me. At cruise, it should be (and indeed used to be) 14.7:1, now it's in the low 14s. Dying sensors read leaner, the ECU trims in more fuel, and the independant WBO2 sensors picks this up as a richer condition. FWIW, 14.3:1 would provide about a 3% hit to fuel economy, and indeed I haven't noticed any major drop in mileage. High LTFT is at 150%, which shows how much leaner it's reading at about 0 psi to low boost (10 psi?) than it expects to see. All of the fuel being dumped in was causing some weird part throttle low boost knock (sensor maxed out), enough that my octane value dropped to 30% and the ECU was running negative timing values at part throttle (no power, lot's of spool and turbo noise, etc)! In fact, now that I think about this, the knock was at 7 psi. I'll bet when it switched from the 150% trim (rich) to the regular open loop table the knock was induced from the huge AFR swing... But I digress.

All of this with NO O2 DTC! And rightfully so, the sensor is still "working." ;) And 1G ECUs have a much less sophisticated diagnostic system than the EVO.

Based on the OP's description of the idle conditions and the blinky gauge behavior, I'd say it's worth looking into. Put a meter on the front O2 sensor signal wire at the ECU (where the blinky gauge is, disconnect the guage for accuracy, and try it with it connected as well to be sure the guage isn't interfering) and look for voltage to be cycling between about .3 and .8 at idle. The sensor takes 20-30 seconds to warm up, after that, it should be working. In fact, turn the key "on" for a minute or two before starting the car to make sure it's up to temp, then you can see how long it takes after starting to begin reading voltage. Somewhere around 150(?) degrees coolant temp it should start to cycle, when it goes to closd loop.

Etc.