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From what I've read, it seems that 18-20 inHg is the normal range for manifold vacuum at idle and engine at normal operating temps. My gauge is reading vacuum above 20 inHg. I know my gauge is probably off a few inHg(I'm looking to get something more accurate, i.e. Stewart-Warner).

Is too high of a manifold vacuum a cause for concern?
 

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My old gauge from VDO would shoe me at 25 or so on decel, but my autometer shows me at about 22 on decel. Idle on the VDO was 22 and on the autometer, it is about 18.
 

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Vacuum too high is no issue. The figures you saw are set low actually. Vacuum reading vary for lots of reasons, altitude (lower), Evap system purge valve operating (lower), variable cam timing control (higher), and idle speed (higher rpm- higher, lower rpm-lower).
R's have dual variable cam timing and will be higher than a comparable 5 cylinder older model without that feature.
P2's have idle speed that is higher when ambient temp is mid 80's and above. 60-75 rpm but it is higher.

Vacuum readings quit being very useful when modern engines starting having added features that affect the readings. Misfires still make the needle "nervous" when idling and blocked catalysts still make vacuum drop excessively when you are at lighter throttle.
 

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I've noticed that my vacuum drops down to 15ish when I have the AC/Heat on is that normal? at idle it's around 20-22 and while driving normal throttle its around 0-10 and if I let off the gas while in D it drops to like 25 and at a stop IE stop light it goes to 20-22 again. This is the first time I've had a boost gauge with a vacuum reading lol. I did notice I needed to buy a thicker line then what my boost gauge came with cause I'm guessing the vacuum sucked it flat lol I have since upgraded too a thick 4mm boost line.
 

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I've noticed that my vacuum drops down to 15ish when I have the AC/Heat on is that normal? at idle it's around 20-22 and while driving normal throttle its around 0-10 and if I let off the gas while in D it drops to like 25 and at a stop IE stop light it goes to 20-22 again. This is the first time I've had a boost gauge with a vacuum reading lol. I did notice I needed to buy a thicker line then what my boost gauge came with cause I'm guessing the vacuum sucked it flat lol I have since upgraded too a thick 4mm boost line.
Yes to ac on and low vacuum :)
 

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Yes to ac on and low vacuum :)
Yes, reason, you are putting a load on the engine. Any load on the engine will drop your vacuum.

I had a 63 Chrysler 300 (letter car) that had a vacuum meter on the center console (factory!) high vacuum = economy... low vacuum = power. On the gauge.

Mine seems to be running a little low compared to some of you, so I may go through and check my vac hoses out pretty soon. I run about 20 at idle (ac on) and run about 10 - 15 while cruising at highway speeds. I have had it go as far as 25" of vacuum on a couple of occasions, but it was only for a blip.
 

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Yes, reason, you are putting a load on the engine. Any load on the engine will drop your vacuum.

I had a 63 Chrysler 300 (letter car) that had a vacuum meter on the center console (factory!) high vacuum = economy... low vacuum = power. On the gauge.

Mine seems to be running a little low compared to some of you, so I may go through and check my vac hoses out pretty soon. I run about 20 at idle (ac on) and run about 10 - 15 while cruising at highway speeds. I have had it go as far as 25" of vacuum on a couple of occasions, but it was only for a blip.
Good to know.


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I had an autometer gauge in my 2008 2.5T and the IPD gen II gauge in my R, after setting the IPD's needle to zero the two gauges read the exact same. 10-15" while cruising on the highway, 23-25" when letting off the gas while staying in gear, 19-21" at idle, 15-17" at idle when the AC kicks in.
 
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