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Discussion Starter · #1 ·
I have been trying to diagnose and remedy this problem for several months, and now I need the to call on the collective knowledge of the group.

It all began when SES illuminated one morning as I was on my way to dealer for routine maintenance. The car was behaving normally on the roughly one hour drive (I've been loyal to the same dealer since moving). I was told that my air intake hose was cracked and the dealer proceeded to replace it. Upon leaving the dealer they told me there appeared to also be a small leak around the DISA, but that it was likely okay for now.

After that the car began hesitating when initiating a highway pass around 2500-3000 RPM. I only noticed it in 4th, 5th, or 6th gear. I assumed this was due to the leak around the DISA and purchased both an upgrade kit for my OEM DISA and a cheap temporary DISA so I wouldn't have to rush the rebuild. Upon inspecting my engine I discovered that the technician had not secured my air box. I ordered the replacement bolts and the symptom improved, but was not eliminated.

I later removed and inspected my DISA and found it to be in good working order, so I did not proceed with the rebuild. I did suffer an intermittent SES with code P0174 (lean, bank 1).

Today I replaced the DISA O-Ring and found no significant change. The SES also returned. I did notice that there is a screw hole immediately below the DISA that appears to have been exposed recently (clean; brass colored threads are visible). My guess now is that something else was missed in the dealers reassembly. Diagrams on REALOEM have not been helpful. Does anyone know what I am referring to or been successful in diagnosing similar behavior? I love this car and would really love to get it back to it's ultra-responsive, confidence inspiring self.

Thank you in advance to all contributors. You are much appreciated.
 

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Is it a uniform bog or more like surging/pulsation? The plastic intake manifold has brass inserts for all threaded fasteners, so if you've got one showing, there's a fastener missing.
 

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2004 330Ci 115k miles
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I later removed and inspected my DISA and found it to be in good working order, so I did not proceed with the rebuild. I did suffer an intermittent SES with code P0174 (lean, bank 1).

Today I replaced the DISA O-Ring and found no significant change. The SES also returned. I did notice that there is a screw hole immediately below the DISA that appears to have been exposed recently (clean; brass colored threads are visible). My guess now is that something else was missed in the dealers reassembly.
In the process of removing and reinstalling your DISA, you should have had to remove two screws, M6x18, with a torx head. If you only had to remove one, then those brass colored screw threads you are seeing may be for the other, missing screw. In addition, when I installed my DISA o-ring, I found the fit to be very snug to the point I used a little silicon grease to help it fit.

And BaliDawg's threads on smoke testing have been very valuable to me.
 

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Discussion Starter · #5 ·
Is it a uniform bog or more like surging/pulsation? The plastic intake manifold has brass inserts for all threaded fasteners, so if you've got one showing, there's a fastener missing.

It only occurs when attempting strong acceleration (merging into a faster lane). The tachometer increases about 250 RPM for about one second and then drop back down and the car accelerates as normal. The behavior is not noticeable with steady acceleration.

I took the car out for a 50 mile drive today. The symptom did not appear until the car was significantly warm, after about 10 miles of driving. At that point I was also able to replicate it in 3rd gear today as well.

Could it possibly be a clutch or transmission issue? An indy shop had told me last year that my pressure plate was worn, but clutch was in good shape (original clutch).
The symptom not presenting when cold makes me wonder if it is possible transmission fluid related?
I have never had to replace a clutch on any car, but I assume any clutch problem would present in lower gears and would not present in the middle RPM range? I'd love to hear input from those experienced with clutch failures.
 

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Discussion Starter · #6 ·
Most likely vacuum leaks. Do a quick and easy smoke test to find them.
https://forum.e46fanatics.com/showthread.php?t=1261077

There's also the infamous 2800 RPM stutter due to a DME software bug, but that won't just show up one day.
https://forum.e46fanatics.com/showthread.php?t=966614

Also, consider doing simple maintenance yourself. Get it done right for free and skip the 1-hour drive.
Thank you Bali. I will try to find time to test myself, but I am bringing the car in to the dealer for an airbag recall two weeks from now and may end up asking them to diagnose.

I used to do most maintenance myself and things went much smoother, but since moving to NYC I just don't have anywhere to work on it. I use a valet garage and repairs in the garage are explicitly banned.
 

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Discussion Starter · #7 ·
In the process of removing and reinstalling your DISA, you should have had to remove two screws, M6x18, with a torx head. If you only had to remove one, then those brass colored screw threads you are seeing may be for the other, missing screw. In addition, when I installed my DISA o-ring, I found the fit to be very snug to the point I used a little silicon grease to help it fit.

And BaliDawg's threads on smoke testing have been very valuable to me.
Thank you for confirming beech. It appears my DISA is properly installed so the screw hole I am seeing must be for the intake hose attachment bracket, which doesn't look to be sitting properly now that you mention it.
 
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