Mark81

Since you seem to know alot about the mechanical workings of Audis, maybe you can answer this question. At about 2200 rpm in cold weather, I get a real moan from the engine which I would describe as NVH. When the temperature outdoors is warmer, this seems to dissappear, or at least is greatly reduced. My dealer cannot help me and I'm not sure if all 1.8T A4's have this problem or if it is just with mine. Kind of embarrassing in a $45,000 car. If you have a suggestion or think you know what causes this, I would appreciate your help.

diagnosticator1

And, regarding the characterization as NVH, is it something you can feel as well as hear?

I can try and help you narrow the possible sources by elimination. I have not heard of a particular cause for the problem as you describe it. The only thing that comes to mind right off is possible intake system acoustical resonance.

Mark81

If I am in 3rd gear at 2200 rpm vs, say in 4th gear at 2200 rpm? If this is what you mean, I will check it out further, but I don't think it matters where my trottle is. It seems to occur at 22oo rpm regardless. I take it you are telling me that this is not normal for 1.8t's with manual transmissions?

diagnosticator1

And, does the sound you describe occure at the speed mentioned and is not present at speeds below and above that rpm? What is the speed range you notice it? It is loudest at 2200, when do you first notice it, rpm wise and at what rpm does it go away? If you need to drive the car to answer, take your time and take notes if needed. Not being able to hear it myself, I'm limited on getting an accurate impression of the problem your having. If the noise is considerably louder than other engine sounds while driving normally, no that would not be normal. Has the dealer confirmed your complaint, but unalble to find the problem, or do they say they don't hear it?

Mark81

....and although it is difficult to pinpoint the exact range of rpm's that it is occurring, it seems to start right around 2100 to 2200 rpm and stops shortly thereafter. The noise is a real droan that resonates throughout the cabin. Quite deafening, especially when cold. The problem is definitely much much worse during cold temperatures. I can't even be sure if it is coming from the engine or possibly the exhaust. Going up or down a hill, it seems to occur at the same RPM. To answer your question about the dealer, I currently have more faith in what you might tell be or what I find out in this forum. In searching in here, there are a number of complaints describing the same thing at similar rpm,s. I have not found any solutions, however one comment was the BPV hose because the turbo apparently spools up between 2100 and 2200 rpm and this is when the BPV opens. Does this make any sense? Here is a post from someone else that I found: "I posted on this last year....seems like alot of people were experiencing a vibration specifically at 2100 RPM, especially in colder weather. Several people had brought their cars to the dealers (including myself) and told that it was "normal". Theories included normal resonance of the 1.8T, exhaust, BPV opening etc. I've had my motor mounts adjusted, changed to copper plugs, converted to APR snub mount all without any effect. The only one solution I've read is to disconnect the middle exhaust hanger. Now that the weather is cold, the vibration is back. Just wondering if anyone had any more thoughts/experience with this issue? TIA." Are you an Audi tech? I will possibly try again today. Thanks,

diagnosticator1

In my opinion, I do not believe that the turbo or DV is the source for the problem you are having. To gain more informaion on the dynamics of the situation, I suggest you remove the APR snub, reinstall the OEM snub, and PRELOAD the snub mount against the pocket in the same direction that the crankshaft rotates. This positioning will cause the snub to become unloaded from engine reaction torque when driving the car. The goal is to determine if it has any bearing on the supposed resonance problem. As a trial, the pre-loading may increase idle vibration in neutral somewhat.
A different area to consider is that the exhaust system MUST me adjusted as explained in the Bentley, there must not be any expansion stresses placed on the exhaust system mounts when the system is at operating temp. The adjustment instructions are specific regarding positioning of the system parts when cold to ensure this is the case. Varify that there are no cracked mounts or brackets.
As a side note, there has been issues of vibration with the 3.0l engine, a TSB was issued describing the implication of the A/C compressor drive. The fix was a modified bracket.

(For what is worth, No, I'm not an "Official Audi Tech", but I have an extensive working background in industrial machinery and marine main propulsion and ships auxiliary systems.)

Mark81

what a snub is and just to let you know, my car is all OEM. No modifications at all.

diagnosticator1

The snub mount is on the front of the engine and controls the torque reaction force of the engine to limit the engines motion on the motor mounts. The "pocket" is the part bolted to the front of the car that holds the shub mount to limit its range of motion. It is provided with slotted bolt holes to allow adjustment.
Is your A4 a manual trans or a TIP?

Mark81

I talked to my Audi dealer today and they indicated that it might be the secondary air valve? Does this make sense?

diagnosticator1

if it has the ability to cause the kind of noise you describe. The only "air valve" that I know of that can cause some noise is the charge air diverter valve. Also known as a boost bypass valve. The Diverter Valve will fail from a tear in the diaphram inside the valve. Pressurized charge air from the turbo escaping through the torn diaphram will make noise, usually a honking type of sound.
Removing the DV and looking into the hose ports may reveal the tear or hole. The small hose port on the top of the DV must hold vacuum or pressure applied at that port and not leak off pressure or fail to hold an applied vacuum. A stock replacement DV is about $40.00.