To get started, first do a visual inspection of all the hoses, clamps and tubes. Look for signs of a pressure leak, such as damp or oily residue around the hose or clamp, bulges or soft spots in the hose, rubbing against another object that could cause abrasions or tears and finally inspect the intercooler core if equipped for indications of impact from gravel or other objects thrown up from the road. Repairs can be as simple as tightening or repositioning a hose or clamp, to replacing torn or damaged couplers.
If your car has over 100,000 miles on the odometer, it is advisable to remove the intercooler and piping, thoroughly cleaning the entire system to remove oil residue and check for any problems. If you have the equipment, pressure testing the intercooler system by making a pressure plug for the front of the turbocharger and applying pressure to the system while it is installed on the car will provide the ultimate way of knowing your system is sealed and functioning properly.
The next item of inspection for the high mileage car will be the oil supply line. Over time this line is subjected to oil flow and of course temperature extremes. The oil will start to turn to carbon in the areas of high heat, and if left un treated can create a detrimental restriction of oil flow to the turbocharger itself. Usually oil supply lines are relatively inexpensive from the dealership, and if your car has over 100,000 miles showing, the line needs to be serviced. Note that this line cannot be reliably cleaned, replacement is the only safe way to complete this job.
While you are servicing the high pressure oil feed line, take the time to inspect all of the oil return line gaskets and connections. Although it is a very important line, cleaning and re-installing is often the only maintenance needed, there is no need to replace the line with a new one unless it is damaged beyond service. The same will also hold true for the turbocharger coolant lines, if equipped.
One question we get asked a lot is how to do a visual inspection of the turbocharger itself. First off, you will need to gain access to the turbochargers compressor inlet. Once you can see the compressor wheel through the inlet opening, observe the area for an excessive amount of oil present in the inlet, or on the compressor wheel itself. The wheel should be a natural aluminum color, with no signs of impact damage or contact with the compressor housing. If it is possible to spin the turbocharger with your fingers, note any resistance or noises. The turbocharger should spin freely, with no rubbing, scraping or other unusual sounds. The turbocharger will have small amounts of radial (side to side) movement in the bearings, but it should never be able to make contact with the compressor housing inlet. Your turbo should have no noticeable axial (in and out) motion that you can feel. If any of these diagnosis fail to pass inspection, the turbocharger needs to be serviced immediately.