Disconnect the battery. Step on the brake pedal. This will relieve any current in the electrical system that maybe present. Reconnect the battery. If you have an Ecutek or UpRev tune. Disconnecting the battery won't affect the tune. What will affect the tune is if the dealer reflashed the ECU with the tune still in it. Then the tune is toast. Sometimes removing the tune and then reinstalling it will help. If not, see your tuner.

Called the tuner and he said the problem is the o2 sensors. He would reflash the car to have EcuTek ignore the o2 sensor reading. He wants to charge me for that.

Sounds like a greedy tuner to me. Most of the good tuners would not have any problems making the quick change to turn off those sensors without additional cost.

I agree it's ******** to have to pay to fix something that should not have occurred in the first place.

Could another tuner use data logging and the current tune to send me a flawless tune through email?

You'd have to send them your tune and hopefully your tuner didn't lock his tune. Are you on Facebook? Contact Eugene Turkov. Here's his phone number. (415) 830-4008 He'll answer until 10:00pm pst. He's in California

Then it won't be possible since he tuned the car on the dyno and flashed it there. Again, could another tuner use data logging on an already tuned for my current mods car to speed up the creation of another tune?

I added the name and phone number to a tuner in my above post. Give Eugene a call. If anyone can help you, he can.

Went to the dealership and the technician verified the harness and it's working. o2 sensor wiring is good too, but the problem may be the o2 sensors themselves (both of them). That or it could be a damaged ECU or a flawed tune. Remind you the tunner wanted to deactivate o2 sensor reading to bypass the issue. Could my problem really be two broken o2 sensors? The technician told me it's very unusual to have both o2 sensor break at the same time.

As for testing the car after the dealership appointment, on cold start temperature the power was back but as soon as the engine gained some temperature it got slow again. I also got the service engine light soon flashing for a brief moment when trying to get to max rpm in 4th gear. The light disappeared as soon as I let off throttle. The technician told me the computer does not read o2 sensor data when the engine is cold but will do once it gets warmer. I think I also got in limp mode because I could barely get to 3000 rpm at one point.

So do you guys think the problem really is the o2 sensors? Dealer will happily sell me OEM sensors but will not accept any return on electronic parts so I must be certain otherwise I'll be stuck with them.

I assume you didn't call the tuner I recommended in my above post?

I just contacted him on FB now. I wanted to have more troubleshooting done at first to eliminate common faults before contacting a tuner to help me figure it out even further.

The good thing about him is he'll help you troubleshoot

Another vote goes to faulty tune
 

Yes he does want to help me! I just talked to him and he thinks the problem is more than likely in the tune. He would check out my data logs and even send me a stock tune file. Thank you for recommending me Eugene Turkov, he really seems like a nice guy. I think I'm in good hands now.

Remove the tune and see if the problem is still there.

Do you have test pipes?

That's what Eugene suggested actually. I have high flow cats, catback and Z1 intakes.

The O2 sensor could have gotten damaged during the install of the cats. A lot of times, if a impact gun was used on the bolts before removing the sensors. The vibrations from the gun will kill the sensors. A lot of people on here have had that issue.