A few things. Use the restroom, get comfy, and have a drink and a snack handy...this is a long one.
If you aren't aware (and I'm not assuming one way or another but I like to cover all the bases), knock is bad and can cause serious engine damage. Knock represents a number of bad conditions that can cause damage to the engine from broken pistons, blown head gaskets, and rods making windows in the engine block as they try to escape. None good. None cheap to fix.
Knock Retard (KR) can be a lifesaver but a tune that doesn't need to constantly rely on it is better since usually you want KR pulling more timing than necessary if knock is detected in order to recover quickly and prevent engine damage. More timing is more power so pulling more than necessary is costing you power that, with a better tune, would give you more power if you don't rely on KR to make up for an overly-aggressive tune. (But I'm making 27 psi of boost yo!)
The more aggressive your KR settings, the more it protects but the more power you lose for a longer time if you see knock. The less aggressive, the more you better hope your tune doesn't generate knock. In my experience, you tune the car so you see 0 KR at Wide Open Throttle (WOT). Some tuners will play with the KR settings like ramp in rate, decay rate, and how much retard is commanded. This is really simplified because even in the simple E67 ECM in the early base models have a few dozen settings you can adjust for KR. Since the idea behind tuning is to optimize and maximize the power you make, most tuners will change these settings to have a less aggressive KR profile and shoot for a tune with 0 kr at the most aggressive boost and timing levels possible. The line between success and failure gets much thinner though when you do this and engine damage can occur in under a second.
For tuning it yourself, unless you have a buddy that is a tuner who can teach you what to do and knows Direct Injection (DI) tuning really well, you are better off letting someone do it unless you have deep pockets to fix mistakes during the learning process. I have done some port tuning but not enough to feel like I will get the most out of my setup. I did the initial tune when I added a turbo to my 2.4 base model and it was drive-able...but taking it to a real tuner picked up about 30 whp. I'm doing remote tuning with Dave Gilbert at PAW using HPTuners so every time he sends me a new tune, I can compare it to the old one and see what he is changing. This helps me better understand what is going on.
Also, I understand the scans...meaning I know what the data means when I look at the scan logs...I understand how the different sensor readings relate to one another and when something looks totally wrong. This helps me give Dave better feedback and what I'm seeing in the tune. If you are new to this and want to learn how to tune, learning how to scan is where you start. What each sensor is, what it does, what role it plays in engine management, how the system it is in works, and what its readings mean in relation to the system and other sensors in other systems.
For instance, An O2 sensor reads the air to fuel ratio (AFR) the engine is running at. You need to know the ECM has a target AFR it is trying to achieve. Let's say that target is 14.7:1...or 14.7 for short. Now say your O2 is reading 16.9...which is lean. Now you need to know that fuel trims will adjust the fuel mixture based on the O2 AFR so you need to see if the fuel trims are trying to add fuel...because they should be. And I said they because there are 2, Long Term (LTFT) and Short Term (STFT). LTFTs are learned over time based on the STFTs. The ECM takes the base fueling, applies the LTFT then applies a STFT based on current conditions. (Again, this is really simplified). So since you are running lean, you look at your Fuel trims. A positive number means it is adding fuel and negative numbers means it is subtracting fuel. You look at them and you see they both are at +22...this is a percentage so your ECM is adding 44% (22% LTFT + 22% STFT) more fuel then it is tuned to deliver! You then look at your Injector Pulse Width (IPW) which is a value telling you how long the injector is staying open. The longer it is staying open the more fuel it is delivering. 0 would be never opening and 100 is open all the time though usually 80-90 IPW we consider the injector to be maxed out. You see yours is at 87.
So the injectors are wide open but still not delivering enough fuel. So you check your fuel rail pressure (which in a Redline at WOT is around 1800 PSI but we are not using those numbers here for a lot of reasons) and you find it to be 60 psi. You know injectors will flow less fuel with less pressure but 60 psi is where the pressure should be. Seeing this scenario in your scan would be a sign that you have an injector issue meaning they are dirty, clogged, one or more have failed outright OR if you are working with a modified car and a custom tune, that your injectors are either too small or your injector tables are WAY off. While this is an example of troubleshooting with a tune (and there would be engine codes in this scenario), this is what I mean by knowing how all this works and what all the data means. This is what you need to know first before you start to try tuning. Mind you, this is just port injection fueling (and direct injection is more complicated). Not air intake, not timing, not cooling, not Volumetric Efficiency (VE) and not boost control...just a few more systems you need to be familiar with.
I am not familiar with the OPs knowledge level but generally speaking, those who know enough to tune don't ask questions regarding which is the better route to go with, buying or making a tune.
Lastly (I swear) every platform is different and while all internal combustion engines have the same basic needs, there are a ton of different ways to do it and this means to tune a particular car, you need to know how the engine management system (the ECM and the Software that's on it. Just like personal computers, a Mac is Different from an IBM and an IBM can run on Windows which is different from Linux...The same ECM can have multiple different operating systems which can have different methods of managing an engine) works and how to adjust it. So if your local tuner isn't familiar with the logic in the ECM's OS and how it works with YOUR engine, they may not be a good tuning choice for you.
I know this is a long read, but these guys will tell you this is normal for me and that I like giving very complete and detailed replies. LOL
