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E46 (1999 - 2006)
The fourth generation 3 Series (E46 chassis) was introduced in 1999 and set the standard for engineering and performance during it's years of production including being named to Car & Driver's 10 best list every one of those years! ! -- View the E46 Wiki

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  #1  
Old 12-03-2012, 03:11 PM
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Clever way to check for vacuum leaks?

I've been chasing an idle surge problem for a few weeks now, although it's hardly been a priority. It's gotten cold out here in NH and I feel like it is related to the temp, but can't say for certain. The car starts normally and idles perfectly cold, then after a short drive e.g. to work, when I clutch in the idle fluctuates from 500 to 1000 and back about 8 to 10 times and then settles down to 700ish, and stays there.

I have cleaned the DISA valve and ICV and replaced both intake boots. The ICV in particular was quite dirty, and the lower intake boot was definitely cracked, but the problem is more or less exactly the same.

My research has pointed me to look for vacuum leaks, but other than visual inspection of the hoses I can see, any thoughts about how else to pinpoint a possible leak?

Thanks in advance.
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  #2  
Old 12-03-2012, 05:51 PM
Jimmys 530i Jimmys 530i is offline
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I just hook up my smoke machine. If I am not at work, I use brake cleaner.
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  #3  
Old 12-03-2012, 06:03 PM
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I use a propane torch and an OBD-2 reader. I set the reader up to graph short-term fuel trim in real-time, turn on the torch low (and NOT lit!), then slowly move the torch around the intake side of the engine. When the fuel trim plummets, the torch nozzle is near the vacuum leak. A bit crude, perhaps, but it works. In the interests of not blowing anything up, don't do this on the exhaust side of the engine.
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Old 12-03-2012, 06:57 PM
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Quote:
Originally Posted by 1972ford View Post
I've been chasing an idle surge problem for a few weeks now, although it's hardly been a priority. It's gotten cold out here in NH and I feel like it is related to the temp, but can't say for certain. The car starts normally and idles perfectly cold, then after a short drive e.g. to work, when I clutch in the idle fluctuates from 500 to 1000 and back about 8 to 10 times and then settles down to 700ish, and stays there.

I have cleaned the DISA valve and ICV and replaced both intake boots. The ICV in particular was quite dirty, and the lower intake boot was definitely cracked, but the problem is more or less exactly the same.

My research has pointed me to look for vacuum leaks, but other than visual inspection of the hoses I can see, any thoughts about how else to pinpoint a possible leak?

Thanks in advance.
Pull the lower vacuum line off the F connector from the intake boot just behind the MAF. There should be a 4 inch piece of 3.5MM vacuum line and about three feet of hard plastic line and then another 4 inches of vacuum tubing where it attaches to the fuel pressure regulator. You may have to cut the vacuum line off the F connector, if it is old and brittle etc, so have some on-hand to replace it. Blow into it and make sure that line is solid / no leaks down to fuel pressure regulator, or you can pull a vacuum on it if you are shy .

Anyhow, that is how you can check that one without jacking up the car and removing fuel filter cover etc. I would also recommend you change all the 3.5MM vacuum line from secondary air pump where it wraps around intake manifold and goes into vacuum switch behind intake, back out to check valve and back into the intake. Vacuum switch is easily detached to make job much easier. There is also a cap/plug back there that can crack.

Check out post six on this link to see what I am talking about.
http://www.bimmerfest.com/forums/sho...134&highlight=

Last edited by QAfred; 12-03-2012 at 06:59 PM.
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  #5  
Old 12-04-2012, 05:41 AM
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Thanks for the advice, I'll give the blow test a try on the small tube at the F connector, that's the easy place to go next. Of course this morning it's 34 degrees (relatively warm) and it didn't do it. I also wonder if there might be any codes stored but no CEL/SES ... I'll give it a quick scan when I get a chance. This is really nitpicking, but since everything else on the car is working so nicely, I want to figure this out. Also I don't like to have any issues going into winter when I rely on the car a lot more. Maybe I'll replace some of the other lines next oil change...
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Old 12-04-2012, 10:21 AM
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Quote:
Originally Posted by 1972ford View Post
any thoughts about how else to pinpoint a possible leak?.
I've tried the brake cleaner - but - for a pinhole leak, intermittent leak, or for buried leaks (such as the lower CCV vent hose), it just didn't work for me.
- Does the order of the misfire OBDII DTCs diagnostic trouble codes actually matter (1)


What worked for me to find the cause of my plethora of non-specific lean-misfire codes was a $30 smoke test!
- How to make your own smoke machine (1)


The result was this underside leak, which the brake cleaner didn't get to:


And, this huge leak, which also the brake cleaner (and presumably propane) can't get to:

Moral of the story:
Based on my one experience tracking down lean misfire codes, I recommend a smoke test or simply replacing all the hoses.
- How to diagnose a BMW M54 engine misfire (1) & a cold-engine intermittent misfire (1)
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See also: E39 Bestlinks & How to easily find what you need

Last edited by bluebee; 12-04-2012 at 10:23 AM.
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  #7  
Old 12-04-2012, 10:44 AM
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I've used both propane and starter fluid. VERY carefully.
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  #8  
Old 12-04-2012, 11:05 AM
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As blue said. Buying a smoke test machine does wonders. I've found every vacuum/boost leak I've had with it.
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  #9  
Old 12-04-2012, 01:34 PM
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Pull the dipstick while it's running and then put it back in. If the engine pitch doesn't change there's a leak somewhere/bad CCV. Also works with the oil fill cap. If there's a leak the car's already idling poorly and you'll hear no dipstick. Removing the dipstick just creates a leak so you can test if the system is tight.
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Last edited by DPP528; 12-04-2012 at 01:36 PM.
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  #10  
Old 12-04-2012, 03:15 PM
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Originally Posted by Scott ZHP View Post
I've used both propane and starter fluid. VERY carefully.
To elaborate on Starting Fluid (aka/"Ether"):

This stuff is *highly* explosive, and heavier than air, which means it will "puddle up", and travel some distance from the source, sometimes reaching a spark of some sort, in which case, you don`t want to be anywhere near it.
Use with caution !
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  #11  
Old 12-04-2012, 11:57 PM
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Quote:
Originally Posted by DPP528 View Post
Pull the dipstick while it's running and then put it back in.
Here's a picture of me running a vacuum test (not a leak test, per se), using the dipstick tube.

All you need is a $5 hose and some water:
- How to test the crankcase ventilation (aka CCV, CVV, PCV, CPV, & OSV) pressure regulating valve system (1)

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Each repair should invariably add to our knowledge base by the process of inexorable incrementalism.
Your job, in return, is to read the suggested threads, where the best people will always add value to those threads, either by pictures or by descriptions, so the next person with the same problem stands on your shoulders.
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  #12  
Old 12-05-2012, 06:46 AM
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Thanks for all the responses! It's been behaving better but not perfectly. This morning I tried removing the oil filler cap with the engine idling, and the RPMs did change slightly, then it seemed to readjust itself quickly. When I put my hand over the hole it would change again, then readjust. It was no more of a change than when you turn on the AC or something, a momentary RPM change then back to normal.

That simple hose-with-water test looks pretty straightforward, although I know there is some vacuum there so I'm not sure I'd gain much from that test. But as always, I've learned a lot from reading the threads by Bluebee. Mostly I've learned that my problem is pretty minor compared to some. But maybe when I've got 6 minor leaks I'll have a real problem.... at this point though I'm not motivated enough to get a smoke test.

On the Starting Fluid/Ether / Propane method - I don't think the problem is significant enough that I would gain anything from that either, to be honest. Also, unless I'm missing something, I would need to have the car hooked up to a real-time scan tool to look for changes in run condition as a result of the "fuel" being drawn in?

I think next oil change I'll take off the plastic covers and do some tugging and poking and looking with bright lights to see if I see any particularly bad looking hoses. My upper crankcase vent hose looks and feels excellent. There's a little buildup in it but that goes away with a good highway run, or leaving it in 3rd on my way to work (10 minutes @50mph). The vacuum lines off the F connector are a little stiff, but appear to be fine. The intake boots are new. I'm thinking perhaps the ICV just isn't working properly, based on how much crap was in there and the fact that I couldn't get it all out in the very limited time I had set aside to clean it. Now that I've done it, I could probably get that thing out in 10 minutes or less, so maybe I'll give it another bath in brake cleaner and get some good scrubbing done on the rotating bit.

edit: @fastBob on the ether: I used to use it in potato cannons and, yeah. Get the mixture a little off, and nothing, but get it right and BANG! We found Static Guard to be much more reliable, although not as powerful.
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Last edited by 1972ford; 12-05-2012 at 06:50 AM.
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Old 12-05-2012, 09:36 AM
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Originally Posted by 1972ford View Post
edit: @fastBob on the ether: I used to use it in potato cannons and, yeah. Get the mixture a little off, and nothing, but get it right and BANG! We found Static Guard to be much more reliable, although not as powerful.
I also made a few potato cannons back in The Day, used the cheapest hairspray I could find as a propellant....it worked great !
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Old 12-05-2012, 10:24 AM
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See that black box to the right of the dipstick in post #6? That is an electrically actuated valve assembly that regulates airflow in the two halves of the intake manifold. If you look closely on top of the intake manifold about midway down the box, you will see a sort of raised area where the valve is located inside the manifold. When it is broken, the symptoms are of a vacuum leak. The car will idle rough, but run ok at speed. You will also notice it not accelerating as well on pushing the pedal to the floorboard. How do I know all this? I just had mine replaced because I had a rough idle and a SES light. Lots of codes about intake, misfire, etc. It now purrs like a kitten again.

Maybe your problem? Just an idea.

Also note that when this part fails, there is a pin that holds the valve itself in place that comes loose. If that pin were to fall out and get in the intake of a cylinder, its bye bye engine.

I got lucky and mine didnt fall out. Whew.

Oh this was in my E46 2004 330Ci BTW.
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Last edited by bmwrocks; 12-05-2012 at 10:26 AM.
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  #15  
Old 12-05-2012, 10:36 AM
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@fastBob - it turns out AXE body spray works well too, but same problem as with hairspray, it smells, umm like burned deodorant - imagine that. Static guard had the least offensive odor.

@bmwrocks - I did take that unit out (DISA) and clean it, it appears to be working properly as far as I can tell.

Again today it's "very warm" (45 degrees) and the car is running 100% perfectly. So we'll see if the cold weather brings the symptoms back.
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