I finally got around to doing the intake manifold this weekend. It was long and time consuming, but not really all that bad. I started off thinking all I had to do were the Gaskets, but it got a little more involved. The intake on the 400 / 500 series is a 2 piece setup(I didn't know). There are 7 maybe 8 #6mm allen bolts that hold the intake to the block. You have to remove the throttle linkage from the rear of the intake(3 x 10mm screws) and you only have to disconnect 1 maybe 2 of the little "elbow" links inorder to get the Intake free. You also have to disconnets / remove the Fuel rail and F.I. wiring harness. Disconnect the Mass Flow sensor and the TBA.Remove the bolt from the waterpump which hold the spark plug wire harness on the drivers side. Remove / disconnect a few addl misc vacuum hoses and its ready to come out. (I know I probably over simplified this but it was really straight forward.
Okay I asked for short cuts and rec'd no replys so i had to learned it the "BEST" way, trial and error.
Remove only those throttle linkage"elbows" which are absolutely necessary. Some are a real pain to get back on. Leave the four #6mm allen bolts that hold the two pieces of the intake together. This wasn't a real issue, but this would have been 4 less pieces to keep track of. Got ahead and replace the two heater hoses at the rear of the engine and you might as well do the upper and lower as well as the little 2" radiator hose which attaches to the intake. Replace the 8 injector seals which are on the injectors as well as the 8 seals that hold the plugs in that the injector seat in.
Dont forget to flush/refill coolant and change the oil as there is minimal mixing when the intake is removed. Make sure you clean the FI contacts and that they are reinstalled properly. One of mine wasn't proberly seated and the car ran like crap till I back tracked and saw it barely connected to #6 cyl. Reconnected it and Voila'.
To find out if you may need to do this(you're probably feeling a slight to moderate miss), buy a couple of cans of aerosol brake cleaner and spray it on ALL you vacuum hoses. (BE SURE TO COVER YOUR FENDERS AS THIS $#IT WILL TAKE THE PAINT OFF. I tried cleaning my brake pads/rotors after a job AFTER I had already replaced the wheels
).Spray it specifically on the under side of the intake fore and aft of the TBA. If the engine stuble/stalls, you could stand to do this. Pickup and acceleration are markedly improved(15-20%).