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Does anyone know how the electronic throttle body works?

Have been working on re-engining my ultima with an AHK Audi V8, but I need to modify the intake arrangement - and as part of that, I'm considering changing the throttle body.
Was wondering how easy it would be to get the RS6 throttle body to work, electronically? Does the throttle body just receive an analogue signal and the PID controller is internal to the TB? Or does it have an external stepper motor driver? Or something else?

I'm not 100% sure about this, but I think the butterfly valve is driven (against spring resistance) by a DC motor using PWM from the ECU to control the force. The body has 2 variable resistor tracks in it (possibly doubled up for redundancy) - I'll have to dig out my autopsy photos to check. One track goes from 0% to 100% resistance and the other goes from 100% to 0% resistance. This allows the ECU to check one against the other for coherency.

The ECU will control the motor using some kind of closed loop control system loop. Might be PID, probably is, but might be a different one. Hard to know without the code.

When the engine is off, the ECU will position the valve to the same position (%) as the accelerator pedal, so you could check the signals to the throttle body with a scope. Get one input on the (probably) PWM signal and the other on one of the resistive tracks, then you can use the accelerator to vary the position and see what happens. I suppose in theory you could log the transient and steady-state responses and try to back-calculate the specific control system used, but it's probably overkill.

If you just want to make the throttle body work then you only need to ensure that it's indeed PWM which is easy to do (assuming your new ECU works in a similar way). We know how the output (position) works.

/According to the wiring diagram, there are only 2 wires going to the motor. This makes me think it's direct PWM from the ECU. If it was anything else, I'd expect separate power feed and control signals.

Thanks. I'll see what it all looks once I strip it down. I do like the idea of electronic throttle.

Finished making the headers for it today, all welded up. So many lessons learnt, if I had to make another set I could do a much nicer job next time.
Nevertheless, I'm not unhappy with how they've turned out for a first go by a bloke in his garage. My tig welding has improved too - by the end of the job, I was starting to be happy with some of the welds. I'm waiting on various flanges and other bits to arrive to starting making the rest of it

You can see why I'm keen to turn the intake manifold round......get it away from the exhausts and nice cold air into the intake....

Looks pretty good to me!

Wish I had your skill set Matt.
Great work mate.

Agreed, they look lovely!

What ECU will you be using?

Thank you for the kind words. Of course, when you've made it yourself, you see all the errors.
If I did another one, I'd weld the first primary pipe up, mirrored each side, to give a static reference to fabricate too. I didn't do that here since clearance was a really big deal and I wasn't even sure what fitted one side would fit the other. But they are close enough that, except for side by side, they look the same.

Been researching throttle bodies. The throttle body on the RS6 is special and somewhat rare, but I can find throttle bodies from the naturally aspirated versions a lot cheaper and many are available. 6 Wires - 2 run the motor, 2 position sensors, 5V supply & ground.
And I've found a drive by wire controller that can run it - it also integrates with the ECU I'm running so I can then have idle advance and other "features" such as full throttle shift if I wanted them.

I could just keep it all simple and stay with the mechanical setup it comes with - but it all looks a bit messy as you can see on the pic above - I like the clean look of the DBW throttle bodies and I think it'll give me some nice options for ducting a nice, cold, clean, air source in.

I'm doing a build thread on pistonheads if anyone's interested : https://www.pistonheads.com/gassing/top ... &t=2065405

Next thing is I'm waiting for the flanges for the secondary pipes to arrive - I can then finish up the secondaries and the X-pipe assembly. I think I'll take a risk and make the x-pipe right up close to the existing TB on the basis that I "can" turn the manifold around - I have found a pic of someone that has done it already, how hard can it be, eh?



You can see he also ditched the mechanical TB too...

Shoppinit wrote: ↑

Sat Mar 09, 2024 10:03 am

What ECU will you be using?

I've done a couple of megasquirts before, so am fairly familiar with them. Didn't really fancy building them from scratch this time though, when I spotted this nicely prebuilt and packaged one

https://www.ampefi.com/product/ms3pro-e ... nt-system/

Awesome. I was looking at MS for my Rangey, but I get the impression that they're not trading any more. No availability on anything.

I bought mine only a few weeks back, from here : https://www.diyautotune.com/product/ms3 ... nt-system/
Better prices.

For a Rover V8, if you're happy with wasted spark and batch fire injectors, an MS2 or perhaps one of the microsquirt offerings, is sufficient - I run both the V8 Landrover and the boat motor on an MS2. But as the Audi motor has a cam sensor, I wanted to go MS3 & Full sequential on the Ultima.

This is the microsquirt - now capable of supporting 4 ignition channels, so fine for V8 Wasted Spark : https://www.diyautotune.com/product/amp ... o-harness/
I might redo the boat with this at some point.

I think that possibly the competitive prebuilt prices, combined with few number of people with the skills to actually build one from scratch means they sell less kits these days.
One reason I went with this ampefi setup is I don't like the enclosures the current MS3 or MS2 kits come with.

Right. I've taken a punt and ordered a DBW throttle controller that integrates with the MS. 50% discount - I suspect once current stock is gone, they'll either be a lot more, or NLA.

Which one did you get?

This controller : https://ldperformance.co.uk/product/dbw ... ontroller/
Which I will pair with a throttle body from the 4.2FSI, part number 077133062A.
Or maybe not - but I think the price of that controller is worth having one "in case".

Looks good. Should work nicely with the Audi throttle body. You're making me want to do the same to the Rangey