That’s the one thing with our smaller engines in the majority of our cars like the A4 where you can have a four-cylinder, as it requires a turbo. Only time it should be a mechanical issue, you would hear engine noise no whining, hissing or possibly clunking sound. A lot of times with the under boost, it’s not able to get to the boost level it requires. When I have the same issue with that part of it and with the P0299 code I believe it is, it was a problem with the diverter valve, or the wastegate. Audi is WORLD FAMOUS for the diverter valve going bad and the P0299 code. But actually each version of the new ones that come out they are getting better and better, I have two version Dee right now which is the best one out. They had upgrades and engineering improvements on the actual valve itself. They still go but the new ones last longer in work much better. In fact if there is a ranking of what’s the number one issue is and more than likely what is two can still happen but least likely I would say this:
1. Diverter valve
2. Wastegate
3. And 75 sensor or the wastegate actuator
4. There are some where is a boost leak
5. It is possible night emphasize possible but not all that likely, as there could be a clogged catalytic converter where the honeycomb grate could be basically trashed inside. Again does happen but highly unlikely.
6. Another could be a few things like some of the linkage in the actuators him possibly the regulator valve, but absolutely without a doubt number one on the list is diverter valves. Especially if you do not have the version D. If you have version eight especially those get incredibly brittle and break and it is more recent, semi recent with the version D which are, so far the highest quality in reengineered valves for the diverter valve.
But again if I had to pick anything with something that sluggish, check engine light, may or may not get a limp mode, and if you do we can kind of turn itself right off and just be random, without a doubt, 1. Diverter valve and 2. Wastegate, bandages really starts to get lower and lower with the N 75 sensor, regulator valve, possible to have those leaks sure, or way way down the list is catalytic converter clogged or damaged. But you can look at the data stream and see your catalytic converter is operating at .999% efficiency
Biggest thing though for anything mechanical and kind of more of a hard core issue is that there’s gonna be some kind of noise associated with the issue you’re having. If it’s running quietly, it’s gonna be one of the above. If you’re getting hissing that’s going to be something with the intake side of the exhaust typically. Any type of whining, or sound like a siren, you’re gonna get some kind of failure in the actual compression. If it’s like a whistling sound that’s an air leak in the charged air ducts, and worst is probably the hissing where that’s more an exhaust leak on the exhaust side of the turbo and more than likely you’re gonna smell the exhaust in the cabin. Do you have any smoke in the exhaust? Maybe not even noticeable to billowing at idle. Lol I mean typically if it’s a black smoke that’s a more of an incomplete combustion right, if it’s a white smoke you’re looking at either coolant, or there’s some kind of moisture in the intake, or have a high EGR rate. But obviously a bluish white is mostly associated with Burney oil, but also could mean a leaky shaft seal for the turbo and you’re burning that oil. Again possible but not likely, or I should say not nearly as likely as the diverter valve and then still in second but way down the wastegate. Lol
Boost pressure sensor or a boost pressure regulator valve (actually called the PCV valve or the crank case vent valve). Not sure if you know of this quick method for testing the PCV valve. If it’s really bad and the diaphragm has been punctured or torn, let the car idle and try and remove the engine oil filler cap or even the dipstick. If there is a tremendous amount of vacuum Making it difficult to pull off the engine oil cap after you turn it, it’s the PCV valve. However you can still have a slight leak with it that’s not going to do that. You can take the engine oil filler cap it’ll pull right off just easily, of course the car will just about to stall out… but… What you will notice is that you burn through about a quart of oil every 3–4 weeks. It’s not getting burned like there’s a piston ring that’s worn and burning through the cylinder, it’s passing through at a slow rate the PCV valve. When you take the breather hoses off, they’ll be some oil residue in there that you can easily see. And if you actually remove the PCV valve, you’ll be able to blow right through it because it’s stuck open). But typically an under boost code won’t trigger a check engine light with just a slight leak and losing oil over a month. It will be something more directly related. They just recently upgraded the valve inside of it, so if you get one make sure you get the upgraded valve. But that gets stuck open or the internal pieces break, it can’t build boost. They’re relatively inexpensive and super easy to change out. Typically you’re gonna have to go underneath the car to do it there’s only three hex bolts holding it on but the only thing is the one on top because of kind of how you have to position yourself in the car can be just a little difficult to kind of get to but changing it itself is pretty easy. But change your mind was what cured mine of that condition. But again typically if it’s a turbo itself or a turbo hardware issue you’re going to hear a whining or clanking sound in most cases. Definitely possible to be leaking or damage charge piping, but I think that’s not as likely either . Obviously there’s going to be a loss of power and like any sensor of any kind on an Audi, even the dang gas cap not on 100% tight or any fluid low, our cars will go into limp mode. Typically I would not consider it something mechanical as well, if you can turn the car off, let it sit and kind of reset, or even unplug the negative cable and let it sit for 10 minutes to reset, typically if it’s going to start working again or at least for just a little bit, I would think it’s more of a valve or sensor than it is something hard core mechanical.
Personally I would think it would be the diverter valve broken or stuck open. Again they’ve upgraded that recently so if you search for the part you can actually put “upgraded diverter valve” and should search for those. To me it’s always seems like it’s less like a valve and it’s more like a woofer the way that the valve acts the same way that a woofer speaker does.
