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Individual Throttle Bodies
- Part 3
Time to tidy up a few loose ends. While I've been very happy with the performance over the last 12 months there have been a couple of details which I've been meaning to address.
Controlling Idle Speed I didn't get around to hooking up the Idle Speed Control Valve (ISCV) when I first installed the ITB's so the idle was set by the throttle stops. This ended up being a compromise between having the car idle adequately when cold and having it idle too high when warm. Invariably it meant a few stalls between backing out of the garage and driving up the street which started to get frustrating. The easiest option was to use the stock ISCV as the wiring is already there so the Adaptronic can control idle speed. The body of the valve has a big hole in the end where it bolted to the plenum so I had an aluminium cap welded over the hole which I then drilled and tapped to screw in a barbed fitting. I shortened the tube on the side and epoxied another barbed fitting into that and it mounts upside down with the electrical connector on the top. Air goes in through a small air filter on the end and the valve controls how much goes out the side which connects into the vacuum lines. Not the most elegant setup but it works and it's all hidden under the top plate.
However, I couldn't bleed air into the vacuum lines which feed the MAP sensor, or the vacuum signal would get screwed up. What I needed was a second set of vacuum lines to supply idle air. I already have a set of vacuum lines on the top half of the manifold so these will have to go underneath.
The tube leaves space at the end for the starter motor and the fittings at the lower left of the image are on the sides of the runners to make room for the water return pipe that runs through the valley. Because these are closer to the valves I've connected this set of lines to the MAP sensor and fuel pressure regulator with 3mm ID hose. The original vacuum lines near the butterflies are connected to the idle air and PCV (via oil/air separator) with 9mm hose and the heater VSV and charcoal canister with 3mm hose. The easiest way to describe all this is with a diagram...
Oil Catch Cans I've used 2 catch cans because the breathers on each cam cover serve different purposes in the positive crankcase ventilation (PCV) system. Standing in front of the car and looking at the engine, the one on the left is a plain breather (air can move in and out) but the one on the right has a valve which opens under vacuum to suck the blowby gasses out of the crankcase and into the intake. These gasses are mainly unburned fuel, but there's also a lot of water vapour and if this isn't sucked out of the crankcase it'll settle in the oil which is not a good thing. When there is high to medium vacuum in the intake manifold (ie. idle to part throttle), some air is sucked in through the left breather (which has already passed through the airfilter and airflow meter if one is in place), dilutes the gasses in the crankcase, out through the valve in right cam cover and into the intake. At wide open throttle where there is no vacuum the gasses can vent out through the left breather and into the intake before the throttlebody (on the Soarer it meets directly under the butterfly). Obviously if we can catch most of the garbage getting sucked out of the crankcase before it gets into the intake, even better. This is where a sealed oil catch can with in and out connections gets plumbed in. Some solvent resistant open cell foam such as that used in fuel tanks does a good job of catching the vapours out of the airstream as it slows down in the larger volume of the can. If you've ever emptied one of these catch cans you'll see why you don't want it in the oil or in the intake - it's mostly brown and gungy water with some oil on top. Another catch can should be installed on the left side and to be emissions friendly it should then route to the air intake after the airflow meter, but before the butterfly. Because I don't have an airflow meter anymore I've just fitted a breather to the top of this one. More in depth info of the PCV system can be found here - http://www.autoshop101.com/forms/h63.pdf
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