I am experiencing a total of 8 error codes on my Mustang's computer. The codes read:

P0135 - O2 Sensor Heater Circuit
P0136 - O2 Sensor Circuit
P0141 - O2 Sensor Heater Circuit
P0155 - O2 Sensor Heater Circuit
P0156 - O2 Sensor Circuit
P0161 - O2 Sensor Heater Circuit
P0443 - Evaporative Emission System Purge Control Valve A Circuit
P1451 - Evaporative Emission System Vent Control Circuit

I do not have catalytic converters so I know this can be provoking the issue. These codes appeared as soon as I replaced my off-road X-pipe with another off-road X-pipe. I had to do this because the first X-pipe was crunched against the frame when bottoming out in a steep driveway. It was night time and I had poor judgement. That is besides the point. Anyways, I had a pair of MIL eliminators on the first X-pipe, but was unsuccessfully able to remove them. Of course these eliminators worked just fine. I then purchased another pair of MIL eliminators. These, however, did not work. All four O2 sensors have been replaced within the past year. I decided to purchase a tuner with Bama tunes in hopes that most or some of these codes would disappear. I do not feel that this is the case anymore. Since I live in Ohio, I am required to have my vehicle emissions-tested every two years. Until I can get these codes to disappear, I cannot renew my vehicle's registration. I cleared the codes and set my Mustang back to its stock tune right before testing it at a self-serve testing kiosk. Apparently, clearing codes and resetting the computer disables readiness sensors. The kiosk read that only 3 out of the 8 available readiness sensors were sending signals to the testing unit. Because of this, I am required to have a tailpipe test which basically sniffs the exhaust fumes. I will fail this instantaneously. How can I fix/remove these error codes?

Reinstall the cats....you gain minimal power from this and the engine, unless you have a real custom tune will likely never run like it is suppose to.

Anytime that many DTC pop up at all at once, thought should be given to something that all of the systems have in common. At the risk of stating the obvious, have you checked the fuses? Especially F2.2 and F2.8? (OBTW, all of the systems above do share the same fuse).

Seems likely the wiring harness was damaged during the "event".

Here's a fuse panel diagram for your reference.
https://www.allfordmustangs.com/forum...1.html#2669271

That is a good point. I have not checked the fuses yet. I will do that. After these codes popped up, my RPM's started to hang/spike whenever I engage the clutch. It's quite annoying. I was thinking this could be caused by a purge control valve that's stuck open.

Just like you said, fuse number 2.2 was burned out. To my surprise, there wasn't a fuse in slot 2.8. I went to AutoZone and picked up a pack of 20A fuses. I replaced fuse 2.2 and put a fuse in slot 2.8. I started the car up and my RPM's shot up to 2000 and stayed there. After running for about 10 seconds, a cloud of white smoke started to billow from underneath the car and from the engine bay. I turned the car off immediately. I pulled fuse 2.8 and started the car up again. The RPM's fell, but were hanging around 1300 this time, but no smoke. I decided to add the fuse back to 2.8 and the spiked RPM's and smoke followed. The smoke is coming from the engine bay nearest the windshield on the passenger side. What could this be?

Note from previous post. I suspect there is wiring damage.

Being that F2.8 controls all four O2 heaters, a partial short on the passenger's O2 sensor would fit the bill.

Look for anyplace that the wiring harness may have gotten pinched when the exhaust was crushed. Also check to see if the smoke is coming from a burning wiring wiring harness.

So how long have you worked on this problem? Was the advise helpful?

I forgot to mention that I had MIL eliminators placed on the rear O2 sensors. I decided to pull these off. I believe these were the culprit of the shorting because there was a burnt, black hole on one of the eliminators. I placed a fuse in slot number 8 and started the car. The RPM's immediately fell down just below 1k. There was no smoke either. I then hooked up my tuner and cleared the DTC codes. I drove the car on the highway for about 30 miles. The codes have appeared again. I will hook my tuner up and scan the codes this evening. Your advice has helped me. Thanks!

After hooking up a scanner, only two codes were found. These two codes being P0171 (System Too Lean) and P0174 (System Too Lean). I looked under my hood when the engine was running and heard a hissing noise. I found a weathered, cracked hose coming off of the passenger-side valve cover. I'm not sure what this hose is called, but it I replaced it with an 5/8" hose from O'Reilley's. My RPM's finally started to drop at idle and between shifts! However, I still notice very minimal hang time between shifts and sometimes a spike of 100 (not thousand) RPM or so. Could this be from the stage two clutch I have installed? My throttle body was recently cleaned. I am going to clean my mass air flow sensor and idle air control valve. Any suggestions on what other things I can check/clean in regards to make the RPM's fall?

Have you recently disconnected the battery? If so, it's normal for the idle to be rough until the PCM re-learns new idle trim settings. Give it some more time.

If still an issue, start over with the idle/IAC trouble shooting steps.

https://www.allfordmustangs.com/forum...9.html#2260649

Thank you very much for all of your help!