Oh man, that sucks. I'm really sorry to hear that.
When you say "literally everything", that's pretty open ended, since there was a lot of "If, then" statements in my post.
Does that mean you ran all the diagnostics and literally everything came out needing to change, that you ran the diagnostics and only changed a few things that tested bad, that you replaced all of the things I listed without running the diagnostics, or that everything tested good and you couldn't figure out what the problem is?
It seems like you're still throwing parts at it instead of running diagnostics, if you threw a head gasket at it without running a leakdown test first, but I might just be missing context here.
Have you checked the timing and VVT system yet? That VVT cam gear actuator can be a silent killer.

 

I followed pretty much everything. I found out that the new ignition coils i bought were testing .2 resistance higher than the recommended so i put the old ones back in and it didn't change anything. My spark plugs were gapped properly and I tested them and the spark was perfect. The crank and cam sensors both tested normally. My buddy took a look at the spark plug wires (hes ase certified and has worked in a shop his whole life) and said their perfect. I replaced the vvt solenoid which DID get rid of one of my codes. I tried to replace bank 2 sensor 1 o2 sensor but realized i had to drop the whole exhaust system to do it so i decided against it. I also checked the timing and it was perfect. And i checked a few other things. It was good i replaced the headgasket though because the one i had was forsure gonna blow if it didn't already, it was starting to crack. I was actually driving from my house to my girlfriends and it drove fine all the way until i got off the freeway where it did the stutterii had mentioned before and i had to glide into a parking lot because it stalled out. I was cranking it for about 20 minutes before the battery died, it would start but it'd idle super low misfiring really bad and than just turn off, i think i got it to run normally by pressing the gas ONCE than it just completely cut ignition. When i called a shop they said "oh im pretty sure that i know exactly whats wrong with it" and wouldn't tell me obviously because they won't make money than. So i just had it towed to the shop. I have a diagnosis on Tuesday than in gonna get it repaired, im really truly hoping that its not expensive but im sure it will be.

 

I found the problem but haven't fixed it yet. For 1 the crankshaft sensor cable was frayed so the shop it was towed too re-did the wire to connect properly and remade the harness. I ran codes and saw i had an IAT code and an O2 code, aswell as a Misfire on cylinders 4-5-6. Tested the ignition coils and turns out 2 of the oem coils were bad so i replaced them with 2 of the new ones i had gotten that tested good. Misfire disappeared but it still ran poorly on low rpm with bad mpg and less than normal acceleration. Im replacing bank 2 sensor 1 o2 sensor tomorrow to see if that helps, than if it dosent ill replace the MAF since the IAT is integrated with that. That will be the last of my engine codes and if anymore pop up after im just gonna give up. I again am extremely helpful for your help because this stuff was impossible to figure out online until you came around. Your genuinely a life saver i cant say thank you enough.

 

Don't give up if the code is a VVT code, that'll basically just be your solution. I'm currently putting together a guide on how to do VVT system diagnostics.
One of the reasons it can feel like playing whack-a-mole is because all of these systems are so interconnected, so when one system goes down, it can have a hard time figuring out if the other systems are okay or not (ex. if the crankshaft sensor is gone, it has nothing to compare the camshaft position to, so it won't be able to accurately determine the camshaft position). So basically, you fix the crankshaft sensor, suddenly the crankshaft and camshaft can talk to eachother again, and now the computer knows if timing's good or not.

Overall, though, it sounds like you're narrowing in on it. As far as the rough idle, that absolutely could be the IAT code, since you're right, the MAF is tied to that. Get an OEM MAF, I saw someone get a terrible lean condition once because they got an aftermarket MAF that wasn't sensitive enough. It's part number 2220422010, there's a TON of Toyota model's that use it, it's super easy to find. Just bring a multimeter to a junkyard and go in the general direction of any Toyota product, you'll probably find a working one within 30 minutes. I'm supposed to tell you to buy new, but lmao who cares if it works it works

If that's not it, then I'd go back to triple-checking fuel trims to see if there's a vacuum leak, now that you know you have a good MAF reading and good fuel delivery (assuming you went back to functioning stock injectors and checked fuel pressure at some point).
Hopefully seeing how much more simple the diagnostics for this issue are than what you were dealing with before will give you the strength you need to not give up!

But yeah, it always sucks when we end up having to chase down these sorts of sensor issues, but hey, this sort of stuff would have already killed any given newer Nissan or American car by now, if it makes you feel better.

 

Long story short, in the process of fixing bank 2 sensor 1 o2 sensor i found out the exhaust was rusted to **** and it snapped a downstream o2 sensor and the entire exhaust. Downside i lost a o2 sensor and part of ky exhaust, upside my buddy did some redneck science and did some wizzardry with a resistor or something and that o2 sensor reads perfectly normal while being ziptied to the frame. Another upside i no longer have any engine codes, and turns out the "low/rough" idle is actually how it supposed to run as i got in contact with the original owner and its basically just a ghost cam. Another upside is that im running only headers waiting on my eBay exhaust and it sounds like im driving a old school v8😂 its terrible for the motor i know but its only for a week or 2 until the exhaust comes in. Only drive it a few miles a day too and from work so it should be fine... Hopefully...

 

This sounds like the type of fixes I do on the work truck to keep it from dying lmao
Those fixes have caught up to me and now I'm doing a bunch of engine work and a full front suspension rebuild, none of which I really have the time or money for. Be careful what you let become a habit when it comes to "good enough".

 

Hi buddy please did you finally get this fixed I have the same issue currently on my 07 is350 but I only have a battery temperature circuit high code and h02S low bank 2 sensor 1 code

 

What're the actual codes? I didn't even know the 07 IS350 had a battery temperature sensor.
Those codes sound like they're just bad sensors, have you tried testing the sensors and seeing if they're good?

 

I’m so sure they don’t have battery temperature sensor cause have seen a few IS250/350 that doesn’t have one, I don’t know which sensors to check but my car keeps stalling off intermittently and I get this stuttering sound from exhaust when I first go in drive with a fluctuating rpm. I’m yet to check my spark plugs which I will do tomorrow I washed off my MAF sensors this morning but still remained the same the car trips off faster with the AC on.

the actual codes p0051 p0517 p1551

 

The first code is normal, but the second two codes are nearly unheard of on any IS model. They aren't even in the service manual. Those codes're usually associated with hybrids.
To find out if those codes are legitimate, you're probably gonna have to do some sleuthing in the engine bay. I'd test the battery and alternator with a voltameter, then back probe the alternator sensor and, if you can find it, the battery current sensor.
In my experience, only thing it could be other than the alternator, battery, or one of the sensors connected to those two things, is the ECU, unfortunately, and unfortunately, the equipment to test your ECU is usually more expensive than getting a junkyard ECU and spending an hour on the forums learning how to reprogram it.
O2 sensor heater circuit codes are usually legitimate, and usually mean an O2 sensor replacement. Might hold off on that, though, if you're dealing with electrical codes you might just have a weird electrical fault.

 

I just tried to check the car now and I have p1603 code and p0504 code also car keeps tripping off still

 

Well that points us much more in the direction I was thinking. It's an electrical or computer issue. Those codes mean one of two things; either there's a problem with your ECU/TCU, or you have an electrical issue. Often times, those codes can pop up after the battery has been disconnected for an extended period of time and clear themselves eventually.
I'd check the wiring between the ECU and the TCU, and also still do what I said before, which is check your alternator, your battery, the connections between them, and the connection from the alternator to the ECU. While you're at it, it'd be a really, really good idea to check all your ground wires.
Here's a diagram of where to find the ground wires on your vehicle: