This DIY shows how to install a cold air intake on your 01-05 Civic in 6 easy steps. You will need the following tools: a ratchet, a 10mm socket, a 10 inches socket extension, a jack and a jackstand. Figure 1 shows how the engine bay looks like with the stock air intake before the installation.
remove the air inlet duct as shown in Figure2 by removing the 10mm bolt (red arrow) and pulling out the two two rubber pins (green arrows) from the air inlet duct, then pulling the air inlet duct to the left off the intake resonator
remove the four 10mm bolts (red arrows) then pull out the air intake resonator as shown in Figure3.
remove the two 10mm bolts (red arrows) that hold the air filter housing in place, then losen the clamp (green arrow) and pull off the hose that go into the valve cover as shown in Figure4.
disconnect the connector (green arrow) that goes into the air temperature sensor as shown in Figure5, then pull the air temperature sensor out of the air filter housing.
At this point, you can safely pull the air filter housing off the air intake.
push the air temperature sensor into the first pipe, then connect the pipe to the air intake and tighten the clamps, then push the connector into the air temperature sensor, then connect the hose between the pipe and the valve cover as shown in Figure6.
Slide the bracket of the first pipe under the 10mm bolt (red arrow) and tighten the bolt to hold the pipe tight in place as shown in Figure6.
connect the second pipe into the first pipe as shown in Figure7, then tighten the two clamps, then slide the bracket of the second pipe under a bolt located close to the transmission and tighten that bolt to hold the second pipe tight in place.
Jack up the car and slide under it to install the air filter into the outlet of the second pipe as shown in Figure8. You may need to readjust the two pipes to fit the air filter in there.
Fugure9 shows how the engine bay looks like after instaliing the cold air intake.
Hope this helps and enjoy the few extra horsepower and the killer sound of your new cold air intake