if stock is 4mm?

I'm thinking the 3.2mm silicone vac hoses I installed are giving me rough idle, and shaking at low RPM. 3.2mm too restrictive?

Not sure if it could cause problem. Did you maybe forget one or hooked it up wrong way? Double check

I've been considering ordering a spool of 3mm siliconized rubber as I prefer it to 100% rubber or silicone. Outlives rubber by 5 times and grabs the nipples, seals tighter/better than silicone. Little more ridgid and slightly heavier than silicone but much less tendency to kink or collapse under vacuum when hot or in a tight curve. Don't know if I'd get enough interest to justify a $430+tax/shipping cash outlay for 200 ft spool. And I'd probably only offer it in 1 foot increments with a 4ft minimum order.

And don't even ask about colors. If you need deco, paisley or day-glo/neon colors to make a fashion statement this isn't gonna work. You can have any color you want long as it's black or black w/blue stripe but NOT both. I prefer longevity and tight fit to accent colors. I'd prefer all black but the Porsche/BMW dealer only offer it with a blue stripe as that matches their service manual's color coding. But the Porsche dealer told me they can get it in all black but don't stock it.

Whatta you guys think/feel? Interested?

Have you taken the time to measure how much vacuum hose we have on our 12v's engine bay, including the hose that goes to the heater core hoses at the firewall (I used a vacuum hose connector and left the rubber hose behind the firewall as is but I replaced all of the hose that is exposed under the hood)?

I would guess that we need over five feet to cover everything in a manner that allows the hose to remain loose enough for comfort--I added from 1cm-5cm to each piece vacuum hose I replaced to allow for looser routing of the hoses and more wiggle room for fingers and tools when working on the car.

and have been back to Porsche twice for more 1' sections. I keep finding little short sections I didn't know were there originally. And with, like you say, looser routing/wriggle room six or even eight feet is probably not out of the realm of possibility. Especially since it's not even Audi-specific. It'll work someplace on every car, truck and RV made for the last 20 years.

Hmmmm, maybe 10ft minimum orders and one foot increments thereafter. Beats paying Porsche $7.15 per foot for "cut-to-size-pieces."

Not sure if that might be a problem, but I'm kind of suspicious of the small black-and-blue one-way valve, which is spliced into the vac hoses between the intake manifold vac source and the intake manifold switchover solenoid. I wonder if that valve tends to go bad after some time. Not sure what effect it would have if this valve didn't work perfectly. Should be easy to test.

i even extended a few sections

if they cut 3ft off for you it's $21.45 and so on. But it is the best vacuum line product I've EVER seen. I have no problem paying for quality. Tho spool-quantity prices would suit me better at 1/3 the cost. But I can't justify $430 for my own use. I'd NEVER use it all.

Geez, I didn't mean for this to sound obscene. :-P

a. It only lets through a small amount of air that is virtually undectable by my finger
b. I don't have enough practice sucking and I couldn't suck hard enough to open the valve.
c. Maybe the valve is broken?