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Help with Jenvey 55mm ITB’s, Idle air control and drive by wire

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I just purchased a set of Jenvey 55mm ITB’s for my Datsun 240Z. I have 3.1L stroker and new JMC head. I tried running idle air control with my previous build using Jenvey ITB’s but couldn’t quite get it to work. Does anyone have any experience with this? See the attached pics to get an idea of what I’m dealing with. The pics show both sides of the throttle plates you can see the idle bypass tract on either side of the butterfly. There is a threaded hole on the top of the ITB that intersects with that tract. The ITB’s come standard with idle bleed screws or alternatively you can swap out with 8mm barbed fittings to run to an idle air control manifold/motor. The only way to deliver air from an IAC motor to the backside of the butterflies is via these barbed fittings. If you insert the fittings all the way in they go to the front of the butterfly. If you pull the fitting back, you will get air to the backside of the butterfly but now the channel is open to the other side of the butterfly, which seems to defeat the purpose of the whole thing. I’m confused…



Attached Files

I suspect your throttles are possibly one of their older designs. It looks like their current design has the bleed screw perpendicular to the bore. You could possibly tap into the manifold runners instead or shorten the nipples and epoxy/RTV the port that connects to the atmosphere side of the throttle.


Actually they are their newest design. They are the same as the 50’s I had a few years ago. I’m not sure why they changed the design since the old design it looks as if there was a bleed screw that was independent of the idle air control fitting.

On the model I have pictured the brass idle air nipple replaces the bleed screw, there is no independent port. The other plug further forward is just to blank the drill entry. https://www.jenvey.co.uk/media/documents/instructions/AFP_I.pdf

The last two sets I were supplied were just like my pic, one set would have been a year ago and the most recent was only a couple of months ago. They were 45 and 48 though, perhaps their thicker wall castings for the bigger sizes use the different design that you have? I guess you will need to contact Jenvey to see if they have a solution for your specific throttles. I dont often need idle air and have never used their specific kit, I have always just tapped into the manifold runners and DIY'd a vacuum manifold whenever I have needed MAP, idle control or a brake booster connection.

Not really relevant to this topic, but while im here I will recommend getting rid of the colvern TPS they supply, I've had 2 fail after a short life on different engines and one would drift with temperature from new. The variohm hall effect one that Link and many others now stock is a direct fit and much nicer.

I spoke with Jenvey today. All of the diagrams they have for idle air control show the old ITB design with independent bleed screws for idle. The ITB’s I have use a threaded angled bleed screw which allows you to adjust air bypass around the butterfly. You can’t use this same hole to do idle air control. To do IAC there are partially threaded bosses located on the underside of the ITB near the manifold that can be drilled and tapped to run IAC. I told Jenvey they should call this out in their diagrams on their website because it’s very confusing. Regarding the TPS sensors — I ended up buying the more expense contactless TPS sensors because I’ve heard they are a lot better. Thanks for all of your help Adam!

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