Quick question folks, does the idle bypass on the Throttle Body cause dramas with idle, tuning, off throttle boost leak on overun etc??

Or do you simply remove it all and put a blanking plate there?

Thanks in advance.

Quick question folks, does the idle bypass on the Throttle Body cause dramas with idle, tuning, off throttle boost leak on overun etc??


Honest answer? I have no idea!

Describe to me what it looks like, and I'll try to tell you how mine is hooked up.

Honest answer? I have no idea!

Describe to me what it looks like, and I'll try to tell you how mine is hooked up.

It's built in to the T/B. It's just a passage that lets air through while the throttle is closed so the engine can idle, it is usually controlled by coolant temp (via wax pallet?). During cold temp the bypass passage allows more air through for cold idle (higher) and gradually reduced air flow as the engine comes closer to operating temp.

Totally blocking off the idle bypass would cause the engine to stall on closing of the throttle I'd imagine.

It's built in to the T/B. It's just a passage that lets air through while the throttle is closed so the engine can idle, it is usually controlled by coolant temp (via wax pallet?). During cold temp the bypass passage allows more air through for cold idle (higher) and gradually reduced air flow as the engine comes closer to operating temp.

Totally blocking off the idle bypass would cause the engine to stall on closing of the throttle I'd imagine.

In that case, I'm 99% sure mine is as unchanged from before the turbo conversion. So in regards to EZ's questions;

I don't have any dramas with idle (no boost is being produced, so essentially my car runs "stock" at idle)

I'm not aware of it causing any issues with tuning.

All "off throttle boost" is vented by BOV anyway.

It's built in to the T/B. It's just a passage that lets air through while the throttle is closed so the engine can idle, it is usually controlled by coolant temp (via wax pallet?). During cold temp the bypass passage allows more air through for cold idle (higher) and gradually reduced air flow as the engine comes closer to operating temp.

Totally blocking off the idle bypass would cause the engine to stall on closing of the throttle I'd imagine.

That's basically the way carby idling works... it uses a wax pellet which melts as the car warms up.

In an EFI, there is a valve in the passageway that opens or closes a bypass around the TB, which controls the idle. This is computer controlled based on an electrical temperature sensor positioned somewhere in the cooling system, usually on the intake manifold.

I can't see the idle bypass causing an issue with idle and a turbo, as the engine speed is so slow that I doubt the turbo would be doing all that much anyway. If you completely remove the idle valve, you will have an uncontrolled idle, which could cause a number of problems, especially when trying to keep a stable idle. It may have an excessively fast idle too, which will cause the car to use more fuel than it should while idling and may result in more chance of stalling the car too.

I am only going by my experience with this sort of idle control, but have not tested out how it operates on a third gen though...

Still running stock hi flowed throttle body with no mods. It won't cause a problem with idle hav done so since day one.

Thanks for the replies. I am pretty versed in the function of the TB and it's ancillaries ;), just checking what the norm was for members who are boosted BEFORE the TB.

Question answered. :thumbsup: