Howsit guys,

I am having an issue with my a5 that is puzzling a few of the people I know,

The car is a 2014 Audi A5 2.0 TDI automatic with 150 000km/93 000 miles on it.

I have owned the car for 18 months and put on about 43 000km/26000 miles.
The car has had all its services including most recently oil service, air filter, cabin filter and fuel filter.

In March this year I experienced what I can only explain as like a misfire/hesitation in the 2000 to 3000 rpm range, no lights came up in the dash and it was very unpredictable as to when it would happen but the constant was that it only happened in that rev range.
I noticed yellow residue laying in the exhaust tip a few days later and assumed maybe it was a batch a bad fuel, I went to a different filling station and filled up and the problem went away in a few days.

Fast forward to beginning of this month, the same thing starts happening.
I assume fuel again and change filling stations, this time doing a full service on the car with fuel filters to be safe.

EXCEPT this time the issue does not go away.

This is what is happening:

• Hesitating/Jerking quite violently between 2000 to 3000 rpm,
• pressing the accelerator harder to force the car to kickdown and push the revs above 3000rpm then the car drives and boosts normally.
• When the car is cold, gentle acceleration up to 1800rpm is fine, pressing the accelerator a bit harder as to accelerate, the car then gives a soft knocking noise, almost sounds like tappets from my inexperienced opinion, if you do not back off the accelerator then it starts the jerking.
• When the car warms up the jerking sometimes goes away and can ride in the above rev range freely with any amount of pressure on the accelerator pedal.

during this month it has gotten progressively worse.

• When the car warms up now the jerking will not go away, if I drive it like Miss Daisy keeping under 2000rpm and not mashing the accelerator pedal then its fine, would never know something is up.
• If kickdown and push through the 2 - 3k rpm range the boost comes on but in batches and pulsing and often does not give full boost.
• If I hold the car in the 2 - 3k rpm range while jerking for a few seconds it goes into limp mode and throws warning light, I scanned it with my OBD11 and it comes up with a P0299 "turbocharger under boost" code, if I clear it I can continue as per above driving.

I have tried experimenting with different driving behaviors to see if I can pin point any specifics and found the following

• In auto mode, If I drive the car hard, like just flat foot it where possible, the car tends to jerk less when driving normal again, not guaranteed though but most times.
• In manual mode, I can drive it with very little jerking... as long as I do not press the accelerator pedal hard from low, I hope this makes sense, like if push the pedal just just hard enough to increase the revs it will go through the entire rev range with a small gentle hesitation and allow me to redline through the gears, If I push the pedal like you normally would when accelerating I might as well close my eyes and imagine I was on a bucking bull at a pub.
• In manual mode, when I gently get it above 3k rpm I can accelerate hard with boost coming on strong and linear without jerking.

I apologize if this sounds confusing, I will gladly add clarity if you ask for more specifics are identify any details I can expand on.

I am used to doing all odd jobs on my own car so I am not completely useless in and around cars.

Like I say I do have an OBD11 scanner basic version and can run graphs or provide live data if you can tell me which value to check.

I highly suspect the N75 valve as I have come across a video on YouTube that so closely resembles this issue.

I hope someone can chime in on what's happening as I do not want to just throw money at parts before having a good reason to.

Thanks In Advance Guys.

 

not sure how to edit original post but the specific clip in the above video starts at 3:34