Spring is an appropriate time to test the function of your airbox thermostat and change it if needed. The thermostat can seize, allowing hot air to enter the air mass meter and dramatically reducing its lifetime. Note that many turbos do not have these thermostats since the turbo itself adds heat to the intake air.

To test the thermostat:

1. Remove the air intake pipe from the grill hole to the air box extension.
2. Start your engine. As the engine warms up, the flapper inside the hole should move to the fully closed position in moderate to warm weather. If it does not, then you need to change the thermostat. See the FAQ for test temperatures and flapper positions.

To change the thermostat in a 90+ car with the assembly inside the airbox (buy a replacement from an aftermarket supplier for about $5):
1. Remove the air box from the car.
2. Spray PBlaster around the air pipe joint where the extension tube enters the airbox. This joint will be very tight.
3. Gently depress the tabs and twist to loosen and remove the extension tube assembly holding the thermostat mechanism. Be careful that you don't crack the tube or the box while working on it.
4. Once this is free, you will be able to see and access the brass thermostat.
5. Depress the spring using either plier jaws or a two-pringed body clip remover tool. Push this down sufficiently to expose the thermostat piston rod.
6. Pop the thermostat out and insert the new one in its place. Make sure the rod goes in the hole at the top of the spring.
7. Clean everything up, lube the assembly with non-silicone lube, and re-assemble.

The only risks are being a little too brutal and cracking the plastic, or breaking an air box clip on removal. Be careful.