Jag Multiple Throttle Body/ Idle Control Question

limeycars · Post by **limeycars** » Sun Aug 20, 2006 9:24 pm

I am putting together a 3.8 Jaguar Mk2, with a pair of TWM SU-flavored TBs, to replace the HIF44 carbs that are in there now.

My question is, does anyone have a recommendation as to how to control idle? Both TBs have provisions for IACs, but the front and rear halves of the intake do not talk to one another. 3 cylinders per carb, or TB.

My choices seem to be either running a remote IAC, perhaps in the Jeep adapter block and plumbing it into the old starting carb tubing underneath the manifold. I hate that thing, with its 6 flare nuts in the impossible-to-reach locations. My hands hurt just thinking about it....

Or, can I simply run 2 IACs? One in each TB? Can the MS drive a pair of IACs? I think I have room to do it this way and it would certainly be easy to wire.

Talk to me, people! Will it work?

Thanks

eliotmansfield · Post by **eliotmansfield** » Tue Aug 22, 2006 12:16 am

where does your vacuum for the brakes (if it has one?) plumb into?, you could T into that with a solenoid (on/off) or pwm style valve.
If the two manifolds are separate,how are you plumbing your map signal?

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MustangSix · Post by **MustangSix** » Tue Aug 22, 2006 6:34 am

While it would seem necessary to plumb the IAC so that all cylinders are equally affected, you could control idle by just adjusting one set. Just as the idle can be (incorrectly) set by turning the idle screw on a single SU, the same effect would be available by just adjusting idle air on one TB.

eliotmansfield · Post by **eliotmansfield** » Tue Aug 22, 2006 11:12 pm

Wouldn't those three cylinders would run marginally leaner than the other three? - Potentially causing a rough idle?

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limeycars · Post by **limeycars** » Wed Aug 23, 2006 2:05 pm

I just checked the intake layout, and there is a balance passage between the two banks of cylinders.

Now I have to decide whether I use a remote IAC or dual IACs in the throttle bodies. Dual IACs would be easier.

Does anyone know if you can split the signal and run more than one IAC with the MS output?

Thanks.

(3.0 board with MS-II, jumpered for IAC.)

Heribert · Post by **Heribert** » Thu Aug 24, 2006 12:53 pm

and since it is a limey car, I guess you want to keep it complicated

But since you have found a balance passage , you will require only one IAC valve . The required air volume for idle is quite low and different flow restrictions in the two banks will not upset the idle mixture between the two banks in any significant way.

The MAP tap off point is interesting . Make sure to get a point which is representative of engine load . Somewhere close to where the servo brake vacuum line is connected to the manifold is a good starting point for both MAP signal and IAC bleed in .

Heribert

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