While I am not too sure about this myself, I heard it's because boxers (like most other molosser breeds) are very muscular, and so they get hot a lot easier than other non-mastiff breeds. However, panting can indicate excitement in any dog, as well as stress.
Sometimes stress causes dogs to pant, but usually heat is the main reason they don't sweat like humans, so that is how they cool down.
Computer controlled, not adjustable. (maybe it is on the older mechanical ones, not sure). If the idle is off, something is wrong.
There is a vacuum leak in the engine. When there is not enough pressure in the air system the car will not idle correctly. This can cause a slow idle, erratic idle, or even a surging idle. Check the vacuum lines and intake for any leaks.
spark plugs
Adjust your idle.
Depends most common on older models is rough idle and or suspension starting to go.
miss alignment of tires
There are several things that can cause high idle. An older carbureted engine may have a vacuum leak or sticking choke linkage. Newer computer controlled engines have an idle control device called an idle motor which could be faulty or receiving bad information from other sensors on the engine ( IE. temperature sensor ).
timing is advanced to far
Large intake vacuum leak or idle air bypass valve stuck open
If the engine is electronic, engine speed at low idle and high idle is controlled by a computer. If it's an older engine, a set of weights and springs work together inside the governor part of the injection pump to control low and high idle. In between these speeds, your foot does the job on the accelerator pedal.
Could be a faulty spark plug or spark plug wire.
Could be a number of things. Does it jump when you are driving it and parked? It could be an idle air control valve or even a throttle position sensor, it could be misfiring also. My t/a did the same and it turned out to be the idle air control valve.