Throttle Body Basics...

[Lion Heart]

Hey guys

Need some practical help here... I'm having issues with my throttle body. Currently always in open position.

BASIC question (hoping not to sound like a fool, lol!!) when you rev the car shouldn't that butterfly valve inside the throttle body be opening and closing as the revs rise/drop?

This is not in gear, just start the engine, idling, rev up and down gently.

Should that butterfly valve be moving?

[StatusRed]

The valve opens more as you press the throttle down allowing more air into the engine to increase power, so yes.

[allanw]

Petrol or Diesel ? If diesel it should be open fully with engine running.

[Lion Heart]

Hi guys

It's the 2.0 diesel.

So it should be open if the engine is running - fully open always???

Surely it must move?

[x DTR x]

When the engine is turned off the flap goes to the open position ready for the next start. That is what i have been told and mine also is always open when the engine is off.

[Lion Heart]

So when does it close?

It seems it's not like a petrol one which opens and closes to control air flow into the engine, diesel is different so that makes a lot of sense.

I noticed if I close it manually the engine tries to stall.

I read that it closes when you switch the engine off to help a smoother engine shut down. Is that right???

I'm trying to work out how I can test if this thing is working and doing what it should :-)

But right now very confused as to when open, when closed?

Someone here said on the diesel it should be open when the engine is running, and again open when the engine is off. So when should the flap actually move?

[Lion Heart]

anyone?

[allanw]

It is also known as an" anti shudder valve" by VOLVO and others e.g. VW-AUDI.
When you switch off engine I believe it should close to strangle the air supply to the engine making for a smoother quicker stop, hence "anti shudder" then reset to open ready for next start. It will also act to kill engine in a run away condition when you switch off. Diesel engines do not have a throttle as such so create no vacuum ( vacuum pump required ) and have constant supply of air and vary the fuel quantity through the injectors for more speed / power. unlike a petrol engine .Of course on a turbocharged diesel more air pushed in by turbo as revs increase. That's the simplified version.

[Lion Heart]

Hi allanw!

Thank you so much for the overview, much appreciated - and yes, makes a lot of sense!!

A question on the Volvo 2.0 diesel butterfly flap. I noted inside the throttle body housing there are cogs (plastic) on the spindle that attach the spindle to the domed 'cap' part which has a breather pipe attached...



In this image note the 'dome' part with the 'gun turret' pointing out at the front, to which the breather pipe attaches.

What makes the flap move? Is it pressure via this breather pipe?????

I thought the throttle body position sensor which attaches to the right hand side in this image (missing) moved it, but I think this is just s sensor/switch and not a motor as such.

So is it pressure via that pipe that moves the flap???

[allanw]

Vacuum "sucks" it closed via the gears you can see. The sensors are the air intake (AIT) sensor and the manifold absolute pressure (MAP) sensor. They measure temperature of air going to the engine and the boost (pressure) air to engine. This info passed on to engine ecu. (engine control unit). Like before this is a simplified version.