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Old 10-26-2012, 05:38 PM   #1
peytonracer4
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i think i have a vacuum leak.

actually i'm 99% positive i do. i have a whistle at certain rpms and a rough idle.
my main gripe is a slow revving engine. it revs like a piece of donkey doo.
when i rev, it seems like it takes FOREVER to return to idle. it reality it doesn't take that long but it does rev very slowly.
i replaced my dirty K&N filter with a poorly fitting paper one. this didn't help.
can a vacuum leak cause slow revving like this? i'm guessing so but someone correct me if i'm wrong.
how do i check for vacuum leaks? how much is a smoke test? my upper and lower intake boots are new. DISA o ring is not but i have a hard time believing it would affect things this much.
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Old 10-26-2012, 06:02 PM   #2
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Isolate the whistling noise dmax style--with a garden hose. start there w/ something simple. I bet its your DISA not sealing correctly. Whatever is affecting your engine is small. Know why? you don't have a code. a large leak would trigger a code for sure. if you had a code, you would have let us know.
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Old 10-26-2012, 10:05 PM   #3
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Solve your misfires, lean codes, rough idle - http://forum.e46fanatics.com/showthread.php?t=897616

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Temp Info - http://forum.e46fanatics.com/showthread.php?t=964491

Hidden OBC Menu - Check Voltage, Temps, Fuel Level - http://forum.e46fanatics.com/showthread.php?t=239619

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Old 10-26-2012, 10:08 PM   #4
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Is your link the disa o ring? I plan on replacing that soon.
Can't see it right now cause I'm on my phone
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Old 10-27-2012, 12:04 AM   #5
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Old 10-27-2012, 01:21 AM   #6
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i checked out the link. BLAH there's so much. i have a feeling i'm going to have a tough time figuring this out.
i'll start with the disa o ring because i've removed and replaced my disa without replacing the o ring. i just have a hard time believing that would be causing my slow revving.
if it's any consolation, i revved my car with no air box on it and it was amazingly fast. not really sure if that means anything or could help you diagnose my issues. don't hate on me, i know it's bad to run the car unfiltered.
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Old 10-27-2012, 04:59 AM   #7
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Without your air box? Did you also have your maf off or unplugged at the time? If so, that also points to air leak...ironically, much more often than a bad maf (though they do go bad, it seems to be quite rare).

What do you mean that the paper filter you replaced your KnN with doesn't fit? Also, if the maf was plugged in, then I'd suggest you clean your maf of the oil from KnN that might have been messed up the maf reading...and it could be as simple as that. I presume you know there's a specific maf cleaning spray.

Was this issue something that happened after you replaced the intake boots, or did you replace the boots to fix this problem?
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Old 10-27-2012, 05:23 AM   #8
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If you're to lazy to go in and poke around for the leak (not saying you're lazy) you can always go to the dealer and have a smoke test run.

+1 on cleaning and inspecting MAF
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Old 10-27-2012, 10:41 AM   #9
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Without your air box? Did you also have your maf off or unplugged at the time? If so, that also points to air leak...ironically, much more often than a bad maf (though they do go bad, it seems to be quite rare).

What do you mean that the paper filter you replaced your KnN with doesn't fit? Also, if the maf was plugged in, then I'd suggest you clean your maf of the oil from KnN that might have been messed up the maf reading...and it could be as simple as that. I presume you know there's a specific maf cleaning spray.

Was this issue something that happened after you replaced the intake boots, or did you replace the boots to fix this problem?
I replaced my k&n panel filter with a paper filter from advanced auto. It fits like crap. I had a really hard time getting the top of the airbox back on.
The k&n fit really really good. It was very dirty and I thought maybe it was the cause of the slow revving.
When I had my airbox off completely my maf was plugged in. I revved the engine for a different reason but I noticed how quickly it revved. Almost like the air box isn't letting the car breathe and removing it fixes the problem.

I'll try cleaning my maf. Makes me kinda nervous because I know how delicate it is.

I replaced my intake boots because they needed replaced. The top one was majorly torn and the bottom one was old.
Despite the huge tear in the upper one, I did not throw a code.

Point of this thread is more to diagnose my slow revving rather than my vacuum leak. However I suspect the two are related. I'm just confused as to why my car revved so well without the airbox and revs like crap with it.

If it helps, I can post a video of how it revs vs my e30 with the m20 engine. Both are stock engines.
My e30 revs much quicker. The rpms drop as soon as I let off the gas. My e46 just kinda goes "blah. You let off the gas? I guess I'll return to idle but first I wanna hangout for a minute"
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Old 10-27-2012, 12:42 PM   #10
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crc maf cleaner...remove maf...just spray, let dry...don't use q-tips or anything and treat the maf gently.

That said, I think I'd try to get the air filter in better. I almost always need to push in the foam rubber edge down to be then able to get the top on (assuming OE air box)...clip done in all three spots. I can't tell you why I think that would make a difference, but it's a known 'issue' as you describe it.

Only other things I can suggest is cleaning the tb and icv (while you're there anyway) and making sure that the tb cable is properly in its bracket.

That you seem to rev fine without air box at all is weird, but the closest thing based on your first post, sure seems to be that issue you had with the filter. OE filter is mann...not sure what autozone is and can't imagine that the quality of paper is so bad that it'd create problems...so I'm thinking mostly that if there's a leak in seam of airbox lid because the filter doesn't seem to fit, that it's disturbing the airflow across maf from what it expects...

Simple enough to play with air filter and see where that gets you...

HTH
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Old 10-27-2012, 12:49 PM   #11
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What I had experienced in my case is that a vacuum leak never caused me sever reaction ... if any at all.

Given the symptoms you've described, I'm surprised you don't have an SES light.

In my case a whistle sound caused by a crack in the lower intake elbow manifest itself in a form of whistle at high, steady speed.

I broke one of the vacuum tubes that runs in the same clips of the O2 sensors' connectors to the cylindric shaped thing, while doing my vcg a week ago. Didn't know about it. 100 miles later it triggered an SES light. Drove for a week without any symptoms at all! Find it last night and fixed it with new vacuum tubing.

Fyi, good idea to have some vacuum tubing in stand by.
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Old 10-27-2012, 04:44 PM   #12
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Throttle body and Icv were cleaned when I replaced my intake boots. My throttle body was clean. My icv was a little dirty but was stills functioning as it should.
I'll try cleaning the maf. And I'll replace the disa deal
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Old 10-27-2012, 05:28 PM   #13
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And work on getting that air filter in properly. Maybe it's the wrong size and the lid itself is leaking, disturbing smooth air flow over maf.

I actually like that weird theory, especially since the way you describe your issue is weird. It runs better without air box according to you. Deal with that filter issue...I'm feeling that's the issue strongly!
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Old 10-27-2012, 07:24 PM   #14
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And work on getting that air filter in properly. Maybe it's the wrong size and the lid itself is leaking, disturbing smooth air flow over maf.

I actually like that weird theory, especially since the way you describe your issue is weird. It runs better without air box according to you. Deal with that filter issue...I'm feeling that's the issue strongly!
My k&n fits perfectly though and I still had all of the described symptoms. I'm gonna poke around tomorrow too see if I can find that vacuum leak. I'll also clean the maf.
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Old 12-14-2012, 12:10 AM   #15
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Hey OP, did you ever find the source of your leak?
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Old 12-14-2012, 01:24 AM   #16
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yea mine is doing the same thing, revs slow and just hangs out before it comes back down to idle....
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Old 12-16-2012, 01:34 PM   #17
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Hey OP, did you ever find the source of your leak?
No. I just ignore it. But the slow revs make it tough to drive manual. It's annoying at times.
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