Boost gauge question

[qduk]

So i noticed something with my recently installed boost gauge. At idle it reads about 18 Hg vacuum. But if the car is moving and I put no pressure on the gas pedal it reads 20 Hg of vacuum. I'm not worried about it or anything I'm just a very technical person and would like to know why this happens...?

[CC'ed]

Manifold vacuum is higher when you are engine braking (moving with the foot off the throttle). normal

[qduk]

Cool good to know. Is 17-19 Hg the right amount at idle? Or could it mean there's a minor leak?

[dingchavez]

I read somewhere that 18-22hg is normal. Normally I idle at 20hg. With AC on however, it dips to 18 hg.

[qduk]

Mine is at 12 with ac on at idle..... What's that mean?

[dingchavez]

Mine is at 12 with ac on at idle..... What's that mean?

Somethings wrong and you're leaking somewhere

[qduk]

Can it be narrowed down because its related to my A/C?

[qduk]

Could it be something with compression inside the engine? Or the A/C pulling to much power for some reason? It still boosts fine. Spikes at 14-15. Holds 11-12. So I'm confused as to why it wouldn't affect psi too. Any input at all would be helpful.

[qduk]

Where do you put a boost leak tester on? The turbo inlet is underneath the car? Is there anywhere I can put one on that would require not getting under the car?

[ElSupremo]

Just had the NewSouth VentPod Boost Gauge installed on my 2012 Tiguan SEL, 2.0TSI engine. Install was done by a local performance shop, but was different from others I've seen. First, an APR Boost Tap was used, which I don't have an issue with (the in-line silver cylinder is an oil filter)



However, rather than installing the sender under the hood (with a subsequently short hose to the Boost tap) and running electrical wires through the firewall, they mounted the sender inside the car in a cavity behind some trim on the drivers side on the outside of the dashboard, as shown.



Now, from looking over some other posts, my readings seems off. At idle - A/C off - I run about 14-16 mm/Hg. A/C on, the reading changes to about 12-14 mm/Hg. Indicated boost seems to max out around +5 psi.

Are these readings ballpark for the 2012 version (Southern California if that makes any difference), or should I (a) be concerned that there's a leak somewhere, or (b) is it due to the long vacuum tube run from the Tap to the sender? I would think that the longer the tube, the lower the reading (more towards 0) for both boost and vacuum, but I'm not sure what the magnitude of this effect might be.

For what it's worth, I also brought the car into the dealer on a "low gas mileage" complaint (~20 mpg with 60 hwy/40 city), but this was before (and after) the boost gauge installation.

[CC'ed]

Length of tubing will not change the vacuum or boost readings. A leak in the tube will.