I have an Evo IX that only has a manual boost controller (set for 23 lbs) and an AWD tune, other than that it's the way it came from the factory. I've never paid attention to what the boost gauge reads at idle, but after I was reading through a random article online it said that typical boost vacuum at idle should be around -10 to -12 lbs? Sometime after reading this article I was in my car and noticed that my boost gauge reads at -40 lbs at idle. It idles smoothly, no issues, it boosts to 23 lbs under full acceleration like it's supposed to, is something wrong or is it okay to have that much vacuum at idle? I went through and checked all of my hoses for vacuum leaks, couldn't find anything that seemed like it was loose, checked the fittings on the boost controller, etc. It idles smoothly at 800rpm when it's warm.

Do I need to be concerned about this? Or is it fine as long as it's running well?

Thanks for any input!

 

that seems like a lot of vacuum . I see about -10- 12 vacuum at idle , maybe you have a bad boost gauge. I wouldn't worry to much if the car is running good and you have no cel.

 

Ever think it may be your boost gauge? If it idles smooth and there is no stumbling or hiccups, you're fine. BTW, vacuum is in in/HG on gauges and not PSI. My gauge usually sits between 12 to 14 in/HG at idle. If you get a loggable map sensor it is actually around -7psi at idle.

 

Thanks for the input, guys! I feel better about leaving it alone then. I'm using the stock boost gauge, so who knows, something might be up with it...

 

I was never aware that evo's came with boost gauges? I have a standard evo 8 , do the mr's come with boost gauge's from the factory?

 

Yessir, my IX MR/SE did. Bottom right gauge in pic (not my pic, but same setup):

 

Thats cool. see you learn something new everyday. I don't know how accurate the factory gauge is on the Mitsu but on my GMC Syclone it a piece of junk and is very in-accurate.

 

You do realize that the stock boost gauge measures vacuum in cm/HG instead of instead of in/HG, and that the boost is in bar instead of psi right? So these are metric measurements and not the standard (U.S. measurements) your used to.

Find a converter online and convert cm/HG to in/HG and i'm sure your vacuum reading will seem more reasonable.

 

I knew about the bar for the positive side, but never noticed that the vacuum side was in a different measurement. I did like you said and found a converter online, so it's actually close to -8 psi, you're absolutely right. Thanks for the input!

 

We here in SA also work on the metric system and your reading looks right.Mine idles at -0.4 bar.Yours is at -0.5 bar.So it's close.

I've got a D1 Spec aftermarket gauge.I actually had to reset my gauge when i bought it because Japan is at a different altitude.

 

That's why the units are listed on the gauge