In my ongoing quest to keep this car running like new, i thought i would post some of the recent mods i did. In addition to these, you should keep your battery and terminals in good condition and inspect ground wires for corrosion. Make sure to check the electrolyte in the battery every several months and add distilled water if needed. most battery have caps that can be pried open to add water. make sure terminal clamps are tight, and wires are securely attached. Anything connected to the + battery must have a fuse to prevent car fire if the wire shorts out.
1. primary oxygen sensor. these are supposedly rated to last 100k miles by honda. I found that after 20k miles, the performance starts to drop noticably. I just switched mine out at 80k miles when the check engine light came on for low response. I suggest not waiting that long. The sensor is only $50 from advance auto and should be replaced between 20-40k miles, imo. it is super easy to change. you just unplug the connector, push out the wire grommets from the stock metal clamps, and unscrew the sensor. jacking up the front driver side of the car made things very easy. i used a cresent wrench and hollow pipe breaker bar to get the old one off, no special tools needed.
here is a pic showing the old sensor screwed in the downpipe just below header (EX) or in the manifold (LX).
for the EX, it is much easier to get to from under the car.
you want to get the BOSCH sensor oem type with connector (part 13532), which is exactly the same as the stock part. It even says NTK on the outside. Be careful when installing the new one. the sensor is extremely sensitive. Do not touch or drop the tip. Keep the OUTSIDE of the sensor free of dirt and liquids. The tip gets old just by being exposed to exhaust gas, but the outside can be damaged too by fluids like antifreeze. always keep it clean. Apply a small amount of anti-seize grease to the threads before installing. Be careful not to get any on the sensor.
You will notice immediate increase in throttle response and decreases idle surge when coasting. The auto trans will shift from R to D faster. and you will get 2-3mpg better gas mileage compared to an old sensor.
2. EGR valve. this thing came stock on all civic EX 01-05 and all 04-05 civics. Its purpose is to recirculate exhaust gas back to the engine in order to reduce harmful NOx emissions and also make the engine run slightly cooler. You can remove it with a socket wrench and extension bar, then spray inside the bottom with carb cleaner. spray until you dont see any more brown/black fluid coming out. Let it dry and then reinstall. Also a great time to paint the lower rusted portion of the valve before reinstalling. You can use a new gasket, but the old one looked fine so i didnt bother.
the car may take a bit longer to start up the first time after this mod, since it needs to adjust to the new conditions.
3. VTEC solenoid. Located on the rear of the engine, it controls when the cam profile switches. It has oil passages and also a screen mesh filter than should be cleaned regularly for optimum flow. A clogged solenoid screen (usually from using a K&N air filter that lets in too much dirt), will cause the check engine light to come on if enough oil is blocked. Engine code P1259 vtec malfunction. There are only 3 bolts holding the solenoid to the engine head. they are shown partially removed below.
there are three other top facing bolts that hold the head on. Should be very easy to remove if you have aftermarket intake. otherwise, you will need to disassemble the stock intake and hardware.
inside of solenoid with filter screen. remove the gasket and clean the screen with a cotton cloth gently. also clean around the mating surfaces and remove excess dirt on the edges.
you can also take off the head and clean around that too. make sure the solenoid button works properly by pressing on it a few times.
4. PCV valve. located to the right of the throttle body down in the middle of the bay, it allows crankcase gases to vent and then recirculate with fresh air in the intake manifold. over time the stock valve may become clogged with oil. Since the valve is entirely metal, you can spray it down with carb cleaner, then reinstall it. it is a simple spring loaded valve and should not need to be replaced. be sure not to lose the washer when removing. First pull off the rubber hose connected to the valve, then use a 17mm deep socket to remove.
5. EVAP canister air filter. Bet you didnt know the car had more than three air filters. (one in the engine bay, two cabin filters, and the evap filter). This one is hiding out in the rear of the car, next to the fuel tank. It has one bolt holding it to the frame, and two hoses that just pull off. be sure to install the new one in the same direction. It is $20 from dealer and i recommend changing it every 100k miles. It was dirty, but not that bad. The filter is part of the vapor recovery system our cars have to burn fuel vapors that are trapped in the evap canister. here it is on the rear drivers side
taken off the car
and cut open just for fun lol
thats all for now...keep your car running its best!
or i could have both 
(roughly...but definitely at least another 75 miles out of a tank!)...better battery = more juice to plugs = better spark?
