Just took apart the EGR solenoid that had failed internally on my car. The process was very simple and it looks repairable.
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Here's what I think is happening inside the solenoids: When I took mine apart, I found a metal "pin" that had fluted sides. It was covered in oil. How does this oil get there? It comes in from the plastic air intake plenum where the black plastic vacuum line attaches to the bottom of the plenum and then to the rear fitting on the EGR solenoid to provide atmostpheric air pressure to help the solenoid close off vacuum to the EGR Valve at idle. This oil gets into the plenum from the crankcase breather pipes that run from the rear of the valve covers to the bottom of the plenum on the left and right.
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It appears that this oil contamination may contribute to the EGR solenoid valve internal failure, as you'll see in the photos below.
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The fluted pin has a spring behind it, and a blue silicone rubber tip. The spring holds the pin firmly seated against the inside of the Solenoid to shut off vacuum during idle. When the computer activates the solendoid the internal magnetic windings are engergized and the pin is held back allowing suction through the solenoid and out to the EGR Valve.
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The silicone tip is imply pressed down into the hollow end of the pin and it actually performs 2 sealing functions. The one I've mentioned when it is rammed forward by spring pressure and then, when it's pulled backward, it's inside seat actually seals off against the inside of the solenoid so there's no suction lost to the atmospheric line.
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Here's where I think the failure occurs. The silicone tip looses it's grip inside the metal pin. When the pin is magnetically pulled back, the solenoid's internal fitting shoves the silicone tip outward away from the pin, and then it gets sucked by vacuum, up against the suction port on the end of the solenoid. This partial, or even complete blockage of suction, kills the suction to the EGR valve. The EGR valve no longer opens or opens enough, and then the computer senses during it's EGR testing, that there wasn't enough hot gasses going past the EGR temp sensor to indicate good flow.......and poof, you get a CEL with "Insufficent Flow" code P0401.
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I think the silicone tip can be glued back in place. I think the solenoid can be either JB Weld epoxied back together, or instant gell glued together, and then it should work correctly again. I also think that the routing of the black atmosphere line needs to not be into the plenum. I think there should be no line at all, and if anything, just one of those little vent caps, that look like a plastic nipple, but they actually have a little channel in the sides, would work great.....and you'd have no more oil residue rotting out the inside of your solenoid.
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Enjoy the photos.
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<img src="http://pictureposter.audiworld.com/57225/1_bend_tabs_up.jpg">
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Bend these 4 tabs straight up using a pair of dykes.
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<img src="http://pictureposter.audiworld.com/57225/2_slide_off_housing.jpg">
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Slide off the metal housing/bracket.
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<img src="http://pictureposter.audiworld.com/57225/3_knock_off_end_plate.jpg">
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Hold the plastic housing in your hand, metal flange down. Slide a screwdriver between your hand and the plastic housing so the tip of the screwdriver rests on the flange. Smack the handle of the screwdriver with the handle of another screwdriver to drive the end flange off. Move the screwdriver around the flange so you get a good even break all the way around.
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<img src="http://pictureposter.audiworld.com/57225/4_blue_silicone_seal.jpg">
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Here's the blue silicone sealing tip.
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<img src="http://pictureposter.audiworld.com/57225/5_blue_silicone_seal_out_of_position.jpg">
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Here's how the silicone tip get's pushed out of position when the metal pin is magnetically retracted by the solenoid.
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<img src="http://pictureposter.audiworld.com/57225/6_plastic_seat_inside_fittings.jpg">
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Here's the hard plastic sealing surface inside the end of the solenoid. It's notched out on one side for vacuum flow, but the silicone tip only seals against the very center area.