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Discussion Starter · #1 · (Edited)
I have a 2008 mazda 3 2.0l automatic. So had an O2 sensor go out, undid the battery. Replaced the sensor reconnected the battery. Check engine light came back on, running lean and same O2 sensor. Deleted the codes drove 200 miles no light, but rough idol when in drive after car reaches operating temp. I attempted to do an idol relearn, but not sure how important turning the ac on is but my AC don’t work. That’s another issue I’m working on as well, should be simple. I just bought this car about a month ago the check engine light was on when I bought it for the O2 sensor (bank1, sensor1) I have been working on bringing her back to life. New struts, shocks, end links, ball joints, front and rear sway bar bushings, tie rod ends, and soon new AC compressor, coil, cultch, and drier. I’ve got all that going but need to figure out why I have the rough idol, any suggestions would be great. Thank you.
 

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Impressive amount of work so far. Did you do the suspension stuff yourself? It is amazing what all this can do for the ride and handling.

Back to your problem. It would possibly help to list your model, engine, year, etc. Also it would be helpful to recheck the engine for any codes since you did your O2 sensor to see if that code is still there. Sometimes aftermarket sensors won't work well especially with the turbo model.
 

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Discussion Starter · #3 ·
Impressive amount of work so far. Did you do the suspension stuff yourself? It is amazing what all this can do for the ride and handling.

Back to your problem. It would possibly help to list your model, engine, year, etc. Also it would be helpful to recheck the engine for any codes since you did your O2 sensor to see if that code is still there. Sometimes aftermarket sensors won't work well especially with the turbo model.
2008 mazda 3 2.0 non turbo. No codes since replacing the O2 sensor. Iv been doing the work myself.
 

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My best guess is a possible vacuum leak. A relatively common place for this is the PCV hose, which is located under the intake manifold unfortunately. It runs right along the engine block and is exposed to lots of heat. I would inspect carefully all the other visible vacuum hoses first and if they all look good it might be worth removing the intake manifold (great video on this on 1AAuto on youtube on a 2.3 Mazda 6 but it's the same process on the 2.0 Mazda 3
 

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... So had an O2 sensor go out, undid the battery. Replaced the sensor reconnected the battery. Check engine light came back on, running lean and same O2 sensor. ... I just bought this car about a month ago the check engine light was on when I bought it for the O2 sensor (bank1, sensor1)...
You need to post all of the actual OBD codes that were read, for everything that's happened in the past. Knowing the codes doesn't necessarily lead to a successful diagnosis, but without them it's total guesswork for anyone reading what you wrote.
 

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Discussion Starter · #6 ·
You need to post all of the actual OBD codes that were read, for everything that's happened in the past. Knowing the codes doesn't necessarily lead to a successful diagnosis, but without them it's total guesswork for anyone reading what you wrote.
I dont have the code took it to the auto part store they ran it and cleared it.
 

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My response is more for a DIY and not necessarily what I would do in the service shop.

Time to invest in a OBDII diagnostic tool. I highly recommend one that plugs directly into the Diagnostic connector and not a wifi device.




While the best recommendation I read so far on this thread was a possible vacuum leak... this also requires a little investment on a large face vacuum gauge that you can plug into any direct engine vacuum port and see how the gauge is responding. You can get these on amazon for about 20 bucks.
One example:
Amazon.com: KUNTEC Car Fuel Pump and Vacuum Pressure Gauge Leak Kit Carburetor Pressure Diagnostics : Automotive



I understand the thought behind wanting to know all the DTCs initially but really it is not necessary. Many times, when one problem generates a DTC if it is not taken care of quickly can cause other DTCs to generate. You may get one or more of the all to familiar undesignated DTC(s) which is caused from a serious of anomalies that are not established in the ECU program. Example the very commonly seen on forums P0300. Having to many DTCs and combined with anomalous generated DTCs becomes a nightmare to properly check all the possible causes. It is easier to note them and then reset the DTC and also go into the monitors and see which are not in readiness and note them. Next clear and reset the Monitors. Then let the engine completely cool down, this way you can be on the cold engine start up procedure from the ECU. Best to let the car sit over night and then restart engine and go for a short drive to get the engine fluids up to normal operating temperatures. As soon as the check engine light is activated quickly check what the DTC(S) is. Then check the monitors again and note anything different from your original observation notation? By evaluating both the newest DTC and the Monitors you can get a better idea where the actual problem is saving a lot of guess work and replacing random parts.

Reading your first post one thing you may want to consider to service is cleaning both your MAP and IAT sensors as well the throttle body. Please use proper cleaning fluids so you do not dame the sensors and follow the direction to the letter. All three can and often do effect the idle performance considerably.
 

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Easiest way to locate vacuum leaks is with a can of starting fluid. Spray a bit around any vacuum hose or connection you can find, if your engine idle increases, you found your leak. Also never hurts to try cleaning your map sensor with a little bit of brake parts cleaner since this plays a big role in you’re fuel air mixture and can also effect idle.
 
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