911 SC Decel Valve Delete

[silverlock]

I've read a ton of reads on deleting decel valves, including:

- https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/797387-deleting-decel-valve.html
- https://forums.pelicanparts.com/porsche-911-technical-forum/1139630-disable-decel-valve.html
- https://forums.pelicanparts.com/porsche-911-technical-forum/755251-decel-valve-vacuum-lines.html
- https://forums.pelicanparts.com/porsche-911-technical-forum/462847-decel-valve-vacuum-limiter-install.html
- https://forums.pelicanparts.com/porsche-911-technical-forum/156181-aav-aar-decel-valve-removal.html

... but they're all a little mixed on the actual mechanics of plugging it (and eventually removing the vacuum line).

1. I have a '78 SC with the decel valve type marked in yellow (no. 14 in the PET)
2. I want to delete it for both driveability and to diagnose/solve the hanging idle issue often attributed to a malfunctioning decel valve
3. It seems the laziest way is to plug the hose (no. 13A) that goes into the "top" (circled in red) of the decel valve, correct?
4. Do I need to plug the nipple on the decel valve itself, or can I leave it open to atmosphere?
(optional) A slightly cleaner way would be to remove the length of hose (no. 13A) and plug that side only the t-socket (no. 14; circled green) entirely, yes?

Is that right?

[silverlock]

OK, update:

1. I plugged the decel valve side of the t-connector
2. I plugged the decel valve itself for good measure
3. Leaving it installed as I monitor.

Fun parts:

- The hose between the t-connector and the TB is very short - the PET is not kidding when it says it's 30mm. It is very, very easy to end up pulling the connector out of the TB side of the hose and having to f-ck around behind the TB/airbox to plug it back in.
- These silicon plugs are nicer than the typical rubber plugs and fit snugly: https://www.amazon.com/dp/B00XYDFW8K?psc=1&ref=ppx_yo2ov_dt_b_product_details

Results:

- Car starts, idles and drives fine afterwards: no immediate issues
- RPM drops like it should now after a blip of the throttle - definitely "feels" more responsive here
- No time today for a real drive before the bad weather kicks in, but expecting a little more liveliness on throttle lift during spirited driving, which is fine for a car that's already a weekend toy with no cats



You can see just the edge of the blue cap behind the TB in this pic: my work light died and I didn’t manage to get a clean pic before I reseated it. The blue cap makes it easier to find in future at least.

[PeteKz]

Silverlock: It looks like you figured it out yourself. I removed mine and used large plugs to cover the places where those hoses plug in to the TB. If anything, my RPM drops too quickly now, requiring me to feather the throttle a bit to prevent he mis-matched RPM jerk.

[proporsche]

you decel valve was(is) way too open...the reason the your idle was hanging high..there is an adjustment to the unit..13 mm open wrench and 7mm to turn the threaded pipe...

Ivan

[silverlock]

Originally Posted by proporsche

you decel valve was(is) way too open...the reason the your idle was hanging high..there is an adjustment to the unit..13 mm open wrench and 7mm to turn the threaded pipe...

Ivan

TIL: I’d seen some discussion on adjustment but the Bentley guide is very thin on it. If I decide to reconnect it I’ll adjust it down - thanks for catching that.

[Bill Douglas]

Ivan, I never knew this. I'd had mine disconnected for many years then when I throttled off to shift gear the revs would drop so fast the engine would sometimes stall. I reconnected it and the car drives fine, but I liked the way the revs dropped not having it hooked up. So I just start turning 7mm and see what happens?

[boyt911sc]

Originally Posted by Bill Douglas

Ivan, I never knew this. I'd had mine disconnected for many years then when I throttled off to shift gear the revs would drop so fast the engine would sometimes stall. I reconnected it and the car drives fine, but I liked the way the revs dropped not having it hooked up. So I just start turning 7mm and see what happens?

Bill,

Set your decel valve to open around 21”Hg and you will be more contended. The reason the decel valve is causing problem is if it is defective (leaking) or opening prematurely at a low vacuum reading.

Tony

[Bill Douglas]

thanks Tony.

[proporsche]

Originally Posted by boyt911sc

Bill,

Set your decel valve to open around 21”Hg and you will be more contended. The reason the decel valve is causing problem is if it is defective (leaking) or opening prematurely at a low vacuum reading.

Tony

Yes Tony..you never know until you try to adjust it..;-)

Ivan

btw you got mail;-)