High vacuum at idle

[95awdboost]

Whats up guys,
my boy got a first gen gsx with big 16g,frount mount, hard piping, full exhaust,turbo timer,boost guage, apexi fuel controller and a hallman mbc....bascially when he turns the car on it idles down at like 700ish but the vac stays between -1 and 0 i know this cant be right because i have two turo cars and niether has a vac that high....you guys got any idea on what coul dbe causing this??

 

[Kait]

check vacuum hoses for leaks

 

[XiKeiyaZI]

The higher the vacuum to better.

What sort of gauge are you using to measure vacuum?

Normally low vacuum means that there is a leak somewhere so the system cannot create an efficient vacuum to build negative pressure. Do a boost leak test and spray EVERYTHING with soapy water.

You can also let the car idle and spray around with starter fluid, avoiding electrical connections. If the idle goes up a when you spray over a certain area then you've found at least 1 of the leaks. Key areas are the emissions hoses, throttle body, intake manifold where it mates to the head, the BISS screw area, and the intercooler piping, of course.

 

[95awdboost]

the higher the vacc the better ?? both my cars vac sits at like -20 around idle and runs smooth as a whistle does that mean i have a issue for vac being at -20..... we're gonna go check over his lines again and ill tell ya what we find

 

[Calan]

the higher the vacc the better ??

No, the lower the vac value, the better (lower pressure reading = more vacuum). -20 in/hg at idle is very good.

 

[XiKeiyaZI]

Suppose a I should rephrase - The Stronger the vacuum (High Vacuum number. IE -20 over -12) the better.

 

[95awdboost]

the guage is a autometer mechanical boost guage.....we sprayed around and the only time idle went up and the vac went down is when we sprayed where intake manifold meets the head, would you guys thing he has a bad intake mani gasket because he says its bolted down all the way....

 

[XiKeiyaZI]

It's entirely possible. For that gasket it can be tricky if you're trying to install it with the head on the car. I always start by snugging the very far end bolts and then tightening the rest down from the inside out - this promote an even seal on the gasket. Just like the head where you bolt it from the center out.

If the surface pressure isn't the same or within reason across the plane where the intake manifold flange meets the head, then it can cause unevenness in the seal/gasket and could potentially allow vacuum leaks and whatnot. I've gone through this a couple of times myself.

 

[95awdboost]

thanks guys now were gonna disconnect everything and see what kinda condition the gasket is in thank you for the knowledge

 

[eclipse420ags]

If all else fails check the TPS.

 

[NHerron]

If the TPS is out of adjustment, it may cause the idle to drop because its output value is different from what the ECU SHOULD see at idle.