I help people diagnose problems with their vehicles everyday. The two reoccurring themes I see in successful diagnoses and repairs, particularly for vexing repair problems that never seem to get fixed, are:
1.) A complete description of the symptoms including how they appeared and the conditions in which they occur are required to sufficiently understand enough about your vehicle problem to make correct decisions about its repair. Be very observant and organize your observations. Note the following about the symptoms:
a.) Did the symptoms appear suddenly or gradually?
b.) Are the symptoms intermittent or constant?
c.) What are the ambient conditions such as temperature, moisture and road condition necessary for the symptoms to occur?
d.) What are the vehicle conditions such as engine temperature, speed, gear, accessories on/off necessary for the symptoms to occur?
e.) Were there any changes to the vehicle such as another repair, or routine maintenance that immediately preceded the appearance of the symptoms?
f.) Are there any things that you can do to change the severity of the symptoms?
2.) A repair technician with modern diagnostic tools and the patience and education to properly use them. Modern vehicles have increasingly more systems controlled electronically. These controls contain computers, modules, relays, sensors and a slew of wiring connecting it all. There is a concert of actions that must occur flawlessly for the vehicle to operate properly. Because there are so many interactions, a fault somewhere in the system can manifest itself as a whole host of problems else where in the system. So, the repair technician you choose to interrogate these systems must have:
a.) Diagnostic tools that are specifically designed for your year, make and model vehicle.
b.) Proper training in the use of these tools. Ask for certifications.
c.) A commitment to thoroughly and methodically sort through the components and make the proper measurements to determine the fault.
d.) A commitment to NOT replace components by trial and error until the offending one is found. Meanwhile, you have paid for all the incorrect tries.
Use of the services of Car IQ will help you do the symptom discovery and find shops that display their education, experience and equipment credentials.