Vacuum leak question...
Thread Starter
Safety Car
Joined: Feb 2003
Posts: 3,848
Likes: 95
From: Springfield MO
Vacuum leak question...
Just finished installing a fast intake on my 98. My question is what does a vacuum leak sound like? The car idles perfect, doesn't miss, and has a smooth idle. But when you raise the rpm's slightly there's a small whistling sound. I've got a vararam also but I'm not quite sure if that's what I'm hearing. The car doesn't lack any power, no codes, etc. Could the whistling sound be a small vacuum leak or am I just paranoid? Any ideas? 
Former Vendor
Joined: Apr 2007
Posts: 1,331
Likes: 4
From: Jacksonville Florida
Just finished installing a fast intake on my 98. My question is what does a vacuum leak sound like? The car idles perfect, doesn't miss, and has a smooth idle. But when you raise the rpm's slightly there's a small whistling sound. I've got a vararam also but I'm not quite sure if that's what I'm hearing. The car doesn't lack any power, no codes, etc. Could the whistling sound be a small vacuum leak or am I just paranoid? Any ideas?
I DO recomend you get a tune if you just installed a fast intake, and youll see even better gains from it
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
I have the exact same issue with a recent install of a FAST intake. Car appears to run fine, but when I crack the throttle you can hear a whistle. I took the instake back off to look for any obvious signs of leaks. I reworked the MAP sensor (remote mount), but still have the same sound. I am going to try spraying starting fluid around the intake with the engine running to see if it affects RPMs. I have a wideband LM-1 hooked up, and when it is cold I am seeing some lean spike at throttle tip in, but this clears up when the engine is warm. So I don't know if it is a tuning problem or is truly a vacuum leak. When my new 30# injectors come in, I will head down to the dyno for a tune, but I want to make sure it isn't leaking before I get there....
Thread Starter
Safety Car
Joined: Feb 2003
Posts: 3,848
Likes: 95
From: Springfield MO
I've got the same symptoms as you. Let me know what you find out. I've tried spraying starter fuild around my vacuum lines, intake base, and around the TB and the idle remains good (ildes the correct way).
Advanced
Joined: Sep 2005
Posts: 83
Likes: 0
From: Santa Barbara Calif
A Chevy Van I had for 7 years with a fast idle that couldn't be fixed.Took it to a different repair shop for smog and what he did
was with an adapter on top of the carb blew smoke into the engine
and the smoke came out below the carb at the gasket and also from
two vacuum hoses to the air conditioning. This was done with the engine not running. The Van never ran better, is alot smoother and the
gas mileage increased, and yes the idle is were it should be, what a
difference a gasket and two hoses made.
was with an adapter on top of the carb blew smoke into the engine
and the smoke came out below the carb at the gasket and also from
two vacuum hoses to the air conditioning. This was done with the engine not running. The Van never ran better, is alot smoother and the
gas mileage increased, and yes the idle is were it should be, what a
difference a gasket and two hoses made.
Advanced
Joined: Jul 2006
Posts: 60
Likes: 0
From: Las Vegas Nevada
I've got the same problem. It's between about 1700 and 3000 RPMs and my car runs fine. I thought it was around the throttle body but couldn't find it. Let me know if anybody figures this out, I am trying to get a dyno tune and don't want to get down there just to find out this whistle won't allow it.
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
Good idea. I had thought about using a smoke stick with the engine running, but I never considered blowing the smoke into the intake with the engine off. I may have to pick up some smoke bombs from the local fireworks stand this weekend.
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
Leak testing with a red plastic tube on the spray can is an OK idea, but if you are going to trial test it by spraying into a vacuum port make sure you hold onto the tube. I let the vacuum suck the tube right up into the intake. After a 2 minute debate with myself, I snatched the intake off and shook the tube out. That gave me another chance to look it over carefully. I took the throttle body off and lapped the sealing surface (it is nice and flat). I snugged it all back down, and the noise is still there. I am going to pick up a stethascope and try to pinpoint the source. It isn't a big deal though because the car is running well. Anyway, here is a picture to document my little excursion today...
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
Advanced
Joined: Jul 2006
Posts: 60
Likes: 0
From: Las Vegas Nevada
Anybody figure anything out on this one? I just got it smoke tested (smoke is pumped into the manifold and checked for leaks) and they didn't find anything. I'm gonna have my tuner check it out before we dyno it on mon. I will let you guys know what he says.
Tech Contributor
Joined: Sep 2005
Posts: 1,731
Likes: 82
From: New Market AL
Last night I disconnected and plugged the vacuum port for the PCV, with no difference in the noise. I may also try plugging the small HVAC vacuum port and the brake booster line to see if that stops the whistle. I am thinking of opening up the intake again to look for internal leaks.
