decel valve really needed ?
 

During the weekend I replaced the top hose going to the decel valve which was fairly loose...
Apparently, as a result of that, idle speed has gone up a bit and decelleration when coming off the throttle, takes way more than it used to be... seems almost like a run of the mill modern gas engine...

Now I know that you can adjust the decel valve rate, but... do we really need it ??
What's the experience around ? If I remove it, a blown airbox is likely ?

I plugged the top hose. No problem.

different models on different years

Removed mine from a 73T years ago without any ill effects.

not needed, mine is gone too. i put a 3.0 throttle body on my 2.7 so it had to go. i found my DV had a lot of oil in it, thus making it not work properly. sometimes it would take longer for the rpm to drop.

that settles it ! Mine will go too when I find the time to do it...
Where did you find the caps to plug the remaining holes ?

There are other components you may have to consider.
Delete Decel Valve plus Thermo Valve plus Diverter Valve?
And disconnect vacuum to the WUR?
Not good.

Why not just check and adjust the Decel. Valve?

if the thermo valve is working i would leave it, especially up north.
diverter valve ?

the vac to the wur is needed.

The decel valve is a smog component designed to prevent the formation of excessive amounts of hydrocarbons during overrun conditions by reducing the amount of vacuum present inside the intake manifold. High intake manifold vacuum during closed throttle overrun leaves the intake charge in a near vacuum condition with very little oxygen to support combustion, thus the formation of unburnt fuel or hydrocarbons.

Since the decel valve is only there to reduce manifold vacuum, it has absolutely no detrimental effects on performance and, in effect, makes as much sense as driving without a gas cap. So why not leave it alone so we can all breath a little easier?

Good explanation... So it isn't just for controlling the deceleration rate...

like stlrj said, Decel valve is an emissions component. My other car (Ford Focus) has a similiar behavor - the revs hang when you let off the gas. The goal is to prevent the engine from going rich immediatly due to the transient fuel still in the intake when the air supply goes away.

The only real "performance benifit" to removing it is the revs will drop much quicker. Depending on your shift times, this may make it easier or harder to shift agressivly. You can always plug the vac line to see if you like the behavior of the car. Note that if your decel valve was leaking then plugging that vac line may require you to adjust your mixtures.

As to the vacuum line to the WUR, I wouldn't remove that. Up until lambda was introduced, the WUR provided vacuum enrichment - i.e. under load the control pressure was adjusted to make the car run more rich for power. I guess you could remove it and just adjust your mix rich to start with, but the vacuum adjustment makes more sense for compromising between economy, performance, and emissions.

If you leave the decel valve alone so the revs hang on a bit longer, your shift times would be better and there would be less wear on your synchros since the revs would match your engine speed to the trans better for each shift.

I'm not gonna remove it. I adjusted the idle back to its normal, and now I don't notice the revs hanging longer than before the decel valve was completely plugged in.