Fast Car

1. Disconnect the negative (black) battery cable from the negative terminal on the battery.
2. Remove the wiring harness from the mass air flow sensor by pressing in on the tab on the wiring harness and then pulling it out.
3. Unscrew the bolts on the mass air flow sensor using a socket wrench.
4. Remove the screw on the air hose clamps on either side of the mass air flow sensor.
5. Disconnect the hoses and remove the sensor. Replace the old sensor with the new one.
6. Reattach the hoses to the new mass air flow sensor and secure them in place by tightening the screws on the clamps.
7. Bolt the new mass air flow sensor into place.
8. Reattach the wiring harness and reconnect the negative cable to the battery.

1. Purchase the correct replacement filter. BMW uses a charcoal activated filter for its 3 Series. You may be able to purchase an aftermarket substitute at an automotive parts store, but you can purchase a factory replacement at your BMW dealer.
2. Shut the engine off and pull the hood release. Locate the cabin air filter cover in the rear part of the engine compartment, right beneath the windshield (it extends to the width of the engine bay).
3. Twist the three fasteners counterclockwise to unhook the cabin air filter cover. Once the fasteners are loosened, pull the entire cover up and set to the side.
4. Pull the old filter out of the compartment. Its clearly visible with the cover removed. Inspect the compartment for foreign items and debris; remove them, if applicable.
5. Insert the replacement filter into the compartment. Position the cabin air filter cover back in place and turn the three fasteners clockwise to secure it.

1. Remove the cowling cover from rear of the engine compartment that covers the firewall. The cowling is secured with screws to the frame of the vehicle. Use a screwdriver to remove the screws and set the cowling off to the side.
2. Locate the cabin air filter compartment on the left side of the firewall, next to the heater fan. The air filter is 6-by-9 inches in size and 2 inches thick. It should be mounted vertically against the firewall. Remove the cover by using a screwdriver to lightly unfasten the lid.
3. Remove the cabin air filter from the compartment. Clean out the compartment by vacuuming out any dust. Wipe it down with a clean damp cloth.
4. Replace the old cabin air filter with the new filter and make sure filter is seated properly. Secure the lid on the filter compartment, making sure the pins snap into place.
5. Reattach the cowling cover over the firewall with screws. Remove all tools from the engine compartment.

1. Connect a OBDII-type engine code reader to your car using the connection port underneath the steering wheel area. Turn the ignition to the on position but do not start the engine. Let the code reader connect with the car computer to see if it will generate a code for a faulty mass air flow sensor. Confirm whether the sensor is actually triggering a malfunction code or not. Erase the code stored in the computer using the reader tools. Turn the car off and disconnect the code reader.
2. Raise the hood and locate the air filter box. Open the air filter box and pull out the old air filter. Use a shop vacuum to suck up all the debris, dust and dirt inside the filter box. However, do not poke the vacuum into the cavity going to the mass air flow sensor.
3. Turn off the vacuum and use a screwdriver to disconnect the hose clamp holding the intake hose to the bottom of the mass air flow sensor going toward the engine. Pull the hose off and place it clear of the sensor. Carefully disconnect the wiring to the mass air flow sensor itself. Use the screwdriver to carefully push the connection tab free if the wiring junction uses a snap-lock to connect. Place it safely clear of the sensor unit.
4. Use a screwdriver with a star-shape, or security Torx bit if the sensor is secured to the air filter box with screws having star-shape heads. Use a regular screwdriver if the screws are Phillips-head or flat-head style. Carefully loosen and remove the sensor screws and put them in a safe place to avoid losing them. Use the shop rag to carefully twist the sensor back and forth by hand until it comes free from the air filter box.
5. Move the sensor unit to a clear workspace. Put a shop rag underneath it and do not touch the sensor mechanism inside. Attach the spray nozzle to your bottle of mass air flow sensor cleaner and spray the sensor clean with five or six good sprays. Spray downward so the excess hits the rag underneath. Examine the wire inside without touching it to confirm it is clean. Let the unit air dry on the rag for 30 minutes.
6. Reattach the sensor, without touching the inside wire mechanism, to the air filter box and following the above removal steps in reverse order. Install a new air filter in the air filter box and close it up. Confirm you reconnected the sensor wiring, re-installed the sensors screws, reattach the air hoses and re-tightened the hose clamps. Check for missing tools as well. Close the hood and restart the car. Let the engine warm up and drive it to check if the sensor gives off a trouble code again. Replace the sensor unit completely if it does.