Ok so lets start at the beginning. 03 audi a4 k03 stock tune.

Car ran great at 10psi wanted to do some simple upgrades to motor get a little more power. I purchased a new cold air intake and air box. Installed and ran great same averaging same 10psi. I wasnt happy with the hoses. Thought i was losing some boost so i redid the hoses off of the intake. Focused on the DV hose going into the intake i re sealed and made sure it was sealed right. First run after adjustment out of no place boost was up to 15-17 psi. Very surprised. Pulled hard fist few gears.Problem #1 Than the DV started making a abnormal sound blowing off very sloppy. #2 boost spikes to 15-17 than drops off as if i let off the gas even though i didnt. While still on the throttle boost will begin to rise and fall all by itself without letting off gas. #3 if i continue to do so i lose boost all together and cant get anything more than 3-5 pounds and traction control light comes on for a second. This is a stock DV we are talking about. Car also has 3" down pipe.... That has been on there for a long time.

Need someone who knows there stuff to confirm my theory.

Boost spikes to much pressure for Stock DV to handle damaging it. Unable to hold boost properly and causing a major leak limp mode activates. only allowing 3-5psi. Replacing DV with ARP r1 DV should do the trick?

Reasoning to believe it is DV besides the sound is if i ride around and keep it under 10psi holds boost enough to not activate limp mode. Or if as soon as i hit 15-17psi release the throttle and dump boost it doesnt go into limp mode. Sound about right?

Lastly did a cold air intake really cause that significant of an improvement to go from 10 pounds to 15 or is something else wrong with the car? Please Help feel free to share ideas could use other opinions. Also after i shut car off and turn it back on boost comes back from 3-5 to 15-17 until it goes into limp mode again. Is that normal? Please HELP. Posted on a few other audi forums to replies. Hoping this one will be a little more help!! Thanks

 

Sounds like your intake either caused the issue or your car has a tune and you fixed whatever was causing it to only hit 10psi. Now your on the right track to replacing stock DVD as they can't handle the higher boost.

 

the reason you are going into limp mode is because you are overboosting. that situation triggers limp mode. it wouldnt trigger limp mode if you had a proper tune. which is what you need before you grande your engine from running lean

i'm not positive, but i think the reason you go from 15-17psi then drops off even though you didnt tought the pedal is because the compturer is protecting itself from overboost. what i think is happening is the ecu opens the n75 which in turn opens the wastegates and bleeds boost down to an acceptable level.

my guess is you messed up on the plumbing. and btw, the hose running from the dv to the intake is only the air being recirculated back into the system. it would affect your boost

 

Well what i dont understand is it was running fine a steady 10psi for a day or so after i put the new CAI on but my DV sounded like it crapped out an was leaking boost so thats when i decided to re seal the seal from the intake to the DV. As soon as i made that minor seal adjustment it started running 15-17 but DV sounded even worse when it released. What would cause a change? You dont believe in any way the can could have already had a tune and the OEM Intake was restricting flow and it just has a bad DV now. As far as a tune goes do you recommend that i have it tuned regardless just to make sure and if so any recommendations. I was considering APR. if you could tell me the steps you would take to diagnose the problem that would be alot of help to. I already purchased a APR DV just waiting for it to come in.

 

check the n75 valve its the T looking valve with a plug in it thats suppost to be connected to the TIP(Turbo inlet pipe).

the n75 valve controls the waste gate function

 

Valve is hooked up just as it was before.

 

Good call on the n75. Simple took a second look and a small hose had a crack in it and was leaking. Problem solved!!!!!!

 

I'm having a similar issue... boost spiking to 15 lbs then limp mode. I did the the test to see if the n75 valve was bad by disconnecting the hose to the waste gate. the car still did the exact same thing. doesn't make sense to me with the boost still spiking and then limp mode that the waste gate could be bad or could it? or is this a sign of a massive boost leak that I can't seem to find?

 

boost leak would set code for under boost.

if you have access to a vacuum pump you can test the waste gate to see if it functions. or you can take a vacuum line and run it to the intake manifold( Must be post throttle body for this to work) and hook it up to the waste gate, start car. at idle the waste gate should open.

secondly if that works, replace n75 with a new one and see if code comes back.

 

I thought my N75 Was good and further inspection found a small crack in one of the hoses. Double check the lines and see if one needs to be replaced. Sounds like the EXACT problem i had.