Since these vehicles are now all over a decade old, making sure they're in good shape before you tune the vehicle and put an extra load on the engine is critical in order to be able to enjoy the car for miles to come.
In addition to keeping up with general maintenance like oil changes, coolant flushes and transmission filter changes, these are some of the most common problems that come up.
With aging rubber and plastic hoses finding a boost leak is a pretty common occurance. In order to track it down a little bit more easily, get a pressurized smoke test performed on your vehicle.
This is the piece of hose that the diverter valves attach into. It has been well documented that this pipe is prone to ripping, and those leaks can cause big tuning issues. It's smart to replace this unit with a reinforced aftermarket unit.
The stock diverter valves are made from plastic. As such over time and constant heating and cooling cycles they begin to break down and leak (and in some cases fail in a spectacular shower of plastic pieces during high boost levels) This is another part we recommend get replaced with an upgraded unit. (like the units from forge)
There are three one-way check valves on the 996 Turbo that typically fail, which cause boost control and AFR issues. The best way to solve these problems is to test and replace bad units before they cause a problem.
The spark plugs should be changed every 30,000 miles with quality replacements, like the NGK PFR7B, and gapped to .027". We do not recommend the use of Iridium plugs in these vehicles as it can cause intermittent issues.
The stock coils are pretty strong and have been used in high horsepower cars, but make sure and check that they are in good physical shape and that if any are cracked they are replaced.