Why the PO disconnected the auxiliary air valve?

[francesconyc]

so while i was working on the AC compressor and cleaning a bit the engine I noticed a disconnected line (clothed hose) that goes to one of those valves on the right side of the engine..

the line is capped with a screw why they did do that? should I put I back? I'm afraid to do it honestly... since the car runs ok...

was it maybe the reason why I have hot start problems??

[john walker's workshop]

The idle was hanging up too long. Common fix.

[AndrewCologne]

@francesco
this is not the "auxiliary air valve" this one is the deceleration valve and does exactly the opposite.

Auxiliary air valve = If the vacuum in the manifold drops, the AAV opens and provides metered auxiliary air when i.E. starting the engine – the unit is on the right edge behind the motor

Deceleration valve = If at deceleration with i.E. closed throttle the vacuum in the manifold goes high, this valve opens, so the vacuum drops and prevents the mixture from leaning out = better emissions (less NOx) and no abitary combustion in the exhaust and so popping at the tailpipe at deceleration. Especially occurring with those lambda based engines as here timing at closed throttle will be retarded by the second vacuum at their dizzy.

[francesconyc]

Originally Posted by AndrewCologne

@francesco
this is not the "auxiliary air valve" this one is the deceleration valve and does exactly the opposite.

Auxiliary air valve = If the vacuum in the manifold drops, the AAV opens and provides metered auxiliary air when i.E. starting the engine – the unit is on the right edge behind the motor

Deceleration valve = If at deceleration with i.E. closed throttle the vacuum in the manifold goes high, this valve opens, so the vacuum drops and prevents the mixture from leaning out = better emissions (less NOx) and no abitary combustion in the exhaust and so popping at the tailpipe at deceleration. Especially occurring with those lambda based engines as here timing at closed throttle will be retarded by the second vacuum at their dizzy.

so in layman's terms... is it ok? what happen if I put it back?

[booyah911]

The PO disconnected mine too. I rebuilt the CIS and reconnected it. If it causes too much rev hang, I'll remove it again. Mine also had a vacuum cap on the decel valve, presumably to prevent vacuum leaks. I would do the same to yours if left unconnected.

[francesconyc]

got it. Andrew is right and i confused the Decel with Aux valve (in the PET book is not really clear)
but since the car runs well I'm gonna leave it as is then! thanks!

[boyt911sc]

Originally Posted by booyah911

The PO disconnected mine too. I rebuilt the CIS and reconnected it. If it causes too much rev hang, I'll remove it again. Mine also had a vacuum cap on the decel valve, presumably to prevent vacuum leaks. I would do the same to yours if left unconnected.

Alex,

A good working decel valve should be closed at 17” Hg (vacuum) or more to keep the vacuum under control. And the valve opens at a much higher vacuum. The lack of understanding how a decel valve works is probably the reason for disconnecting or disabling this CIS component. The early decel valve (pear-shape) is easy to adjust compared to the saucer-shape DV.

Tony

[David Inc.]

I think a lot of these older decel valves just start to fail and replacement prices are bonkers so they just get plugged. I know mine sticks open so I've written it off and enjoy the more freely revving engine and poppity-pops on decel.

[PeteKz]

I removed my decel valve completely (early style, as Tony says, "pear shaped") in order to simplify and decongest the area around the ToD. I don't get decel popping. If anything, the RPM drops too fast for the balky shifting of the 915 tranny.