Steps:
- Pull the fuel pump fuse in the fuse box in the frunk.
- Attempt to start the car until it no longer stumbles and won't start (catch) at all to relieve any pressure in the fuel system.
- Remove the rubber clutch vent tube attached to the airbox cover, if present.
- Remove the engine air filter and airbox cover.
Removing the airbox cover. - During this procedure, I refer to components as front or rear. I use front to mean facing the front of the car and rear to mean facing the rear. Loosen all fittings by rotating them counterclockwise, and tighten them in the clockwise direction.
- Remove the air box. I couldn't get enough clearance for the filter wrenches without doing this.
- To remove the airbox, unplug the temp sensor on the engine side near the top of the box.
- Loosen and detach the vapor hose in the lower left corner of the airbox that runs under the intake manifold.
- Remove the one airbox mounting hex-head cap screw from the top of the box that attaches it to the intake manifold.
MAF Location
On Varioram engine - Detach the Mass Airflow Sensor (MAF) plug
Loosen the clamp band behind the Idle Control Valve that clamps the Mass Air Flow Sensor assembly (MAF) tube to the intake.
Mass Air Flow Sensor
Tube Assembly
Sometimes the clamp is loose enough from previous work to remove the MAF from the intake. In such a case, loosening the band is unnecessary. Loosening the band is a bit of a challenge on the Varioram-equipped engines where it is tucked behind the Idle Control valve plumbing.- On my 1996 Varioram engine, I use a small hex socket on the end of a flex joint attached to an extension rod, slip it in next to the idle control valve, and guide it by feel between the engine insulating blanket above the engine and the MAF sensor assembly. Not fun, but with a little patience it will be done.
- Wrapping the socket tool head and the flex joint to the extension rod with a little electrical tape avoids the tool pulling apart and dropping into the abyss. It also keeps the joint somewhat straight so it doesn't flop around while you line it up with the clamp band adjusting nut by feel behind the idle control valve. Once fully attached, loosen the clamp band adjusting nut just enough so the MAF assembly tube can be slipped off the intake duct. Some find a small flathead screwdriver bit works better than a socket tip because it doesn't require the tool to line up perfectly with the clamp band adjusting nut.
- Access to the MAF and its clamp band is much easier on non-Varioram cars.
The MAF on a
Non-Varioram engine - The MAF-to-airbox mounting bayonet works a lot like removing a lens from an old SLR camera. Turning the MAF assembly counterclockwise about 1/4 turn releases it from the airbox.
- Once the MAF is completely loose from the airbox, you can lift the airbox off its rubber mounting posts and work it out of the engine compartment.
- Stuff a large towel into the space under the airbox & fuel filter to catch any incidental fuel that drains from the filter and to avoid losing dropped tools as you continue.
- Use two hydraulic fitting wrenches in scissors-like action to
release the fuel line (yellow arrow) from the rear-facing side of the fuel filter. Use one wrench on the hex fitting on the filter and the other on the fuel line fitting. Always use two wrenches to avoid twisting force on the related tubes and components, which can cause damage.
Arrows point to the hydraulic attachment fittings. - The hydraulic fitting may take a lot of force to pop loose at first. That is why you use fitting wrenches, not open-end box wrenches that can distort and damage the fittings. Use better-quality wrenches, as inexpensive ones can flex under force and damage the fittings.
- Slightly loosen the clamp holding the fuel filter in place, and use two wrenches to pop loose the hydraulic fitting on the forward-facing side of the filter (red arrow in the picture) and slide the filter out of its mounting band. Be careful to turn the fittings counterclockwise to loosen them. It's easy to get mixed up when fittings aren't facing you, and you are working by feel.
- Once you remove the old fuel filter, replace the fuel-soaked towel with a fresh one so it doesn't stink. To avoid a fire hazard, lay the fuel-saturated towel out on the driveway so the fuel can evaporate before disposing of it.
- Install the new filter, tighten the steel fittings, and secure the clamp band.
- The fuel line fittings are self-sealing if you tighten them down with adequate force; never use any sealant on these fittings, as it can contaminate the fuel system.
- Reinstall the MAF sensor to the intake without tightening the clamp band, attach its wiring, put the fuel pump fuse back in, and start the car with the airbox out.
- It may stumble a bit when starting as the new filter fills with fuel. Once running, inspect the fittings on both sides of the fuel filter for leaks.
- If you see no leaks, turn the engine off and reinstall the airbox. I reinstall the airbox by putting a thin film of motor oil on the end of the MAF where it attaches to the intake,
- Then place the MAF assembly loosely in position without its wire attached, with the sensor's electrical socket pointing up vertically.
- Then install the airbox, attaching the vent hose in the front-left lower corner, and lining it up with the two rubber mounting posts underneath it.
- Then turn the MAF sensor clockwise to lock it to the airbox, moving the up-pointing MAF electrical socket about 1/4 turn toward the rear. In its final position, the MAF connector points slightly toward the rear of the car. Reach into the airbox and verify by feel that the MAF sensor assembly is fully seated into the box.
- Reattach the temp sensor plug to the airbox, and reattach the wire connector to the MAF sensor.
- Reinstall the air box hex head mounting screw and the wire mount under its head.
- Retighten the band that attaches the MAF assembly to the intake. It is a bit of a challenge on the Varioram-equipped cars; I use a small socket tool on the end of a flex joint attached to an extension rod, slip it in next to the idle control valve, and guide it by feel with my hand between the engine insulating blanket and the MAF sensor assembly. Not fun, but with a little patience, you can do it. Wrapping the socket head and flex joint to the extension rod with a little electrical tape keeps the tool from pulling apart. It also keeps the joint somewhat straight so it doesn't flop around while you attempt to line it up with the clamp band adjusting nut by feel behind the idle control valve. Once you achieve good tool contact, tighten the clamp band adjusting nut.
- Install the air filter, then attach the air box cover by inserting its forward-facing pins into the corresponding holes on the front of the box, pivoting the rear of the cover closed, and snapping on the two cover latches.
- Reattach the clutch vent tube if present.
- For safety, make sure all rags and tools are removed from the engine compartment before starting the engine,
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Disclaimer: This blog/website content relates specifically to the Porsche 993 (911 1995 to 1998). The authors are not professional automotive technicians, and some procedures described on these pages may not be best for all situations and may conflict with official factory recommendations. Often, you can learn a lot by simply watching qualified professionals work on your 993. Though we strive to provide accurate and appropriate information on each subject and keep it up to date, some information on the website may be outdated or incorrect. Also, many times the opinions expressed on this site are just that- opinions; therefore, please feel free to use the information on this site at your own risk.
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