What is the throttle valve for ? - Alfa Romeo Forum
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What is the throttle valve for ?

I know, another dumb sounding question.

I was doing some research into my car's juddering issue and logged into the Vauxhall owners website.
It seems there's sometimes an issue with dry joints on the throttle valve pcb, on the back of the main connector

As to what the throttle valve does, (it rarely moves in normal running) it seems it's thought of as working alongside the EGR valve. Some say it stops the engine running on when you switch off...I've never seen mine move.

I operated the throttle valve with AlfaOBD and it seems to respond normally. But curiosity got the better of me . I took the throttle valve assembly off and opened it up and the circuit board cavity was completely flooded with black oil, I can only guess that it has come up through the breather when my dpf was blocked and pressurising the crankcase.

I cleaned it out and not only have I found a couple of dry joints, I've also found a blown IC !
picture here. throttle valve _labelled | Flickr - Photo Sharing!

So I've put it back together and the throttle valve no longer operates with AlfaOBD

The test drive immediately after shows the car still runs great

So, does anyone know when the throttle valve works ?
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I have an older 2.4 10v 156 so what I have to add probably doesn't matter a whole lot to you, but my throttle valve is vacuum-actuated, from the vacuum reservoir at the back of the engine. The throttle valve opens when you crank the engine, and closes when the engine is turned off, as the vacuum stops. It helps stop the engine juddering when it is shutting off, reducing NVH etc. Mine never moved while the engine was running, it just stayed fully open. I've removed mine altogether now, in its place is just straight pipe. I didn't want the restriction there right in front of the inlet manifold entrypoint.

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(Post Link) post #3 of 3 Old 11-11-12 Thread Starter
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Thanks Pud, I've seen that sort of system before. Mine never closed at any time, i watched it while I asked someone else to start, stop and rev the engine !

I've got error codes now, but no EML

I read a thread where a guy just removed the butterfly and swore he could feel a small difference in performance.

It's clearly not a critical part, I'll put it on the things to do list. I haven't got the patience to rework SMD's these days, even though it looks like a common part by ST Micro.
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