FAN OF F1

I will try to make this brief, but fully explain the problem. The car is a well maintained 01.5 with a manual trans. The car was stock with the exception of a cat-back Borla exhaust. About three months ago, I decided to have my 710b valves replaced with 710n valves and install an entire 10 piece Samco hose kit. At that time I also had temp sensor and associated lines replaced to bring the 01.5 up to the 04 pieces. The car was running 100% fine driving it in for the install. After picking it up, the car was falling on it's face at anything over 3500 rpm. It also would occasionally show the ESP/ABS lights when in full throttle when the boost fell off. At the time of this maintenance, it was discovered that the N75 valve had a crack in it. So, I figured the problem was due to a bad N75. I bought an N75 race valve and nothing changed. Same exact symptoms. I then thought that I must have a loose Samco hose, so I did a pressure check and re-checked all hoses. Pressure check tests out fine and all hoses look good. I was also occasionally getting a CEL for an O2 sensor, so i had that O2 sensor replaced. All of this, still same symptoms. The car is not throwing any codes other than the O2 before that was changed, but the car does not run correct at all. I also took the 710ns out of the system and plugged the lines to see if I got a bad valve. Same symptoms with the 710s removed from the system.
Here is the weird thing, the car very occasionally runs strong and appears to have full boost for a couple of pulls. Then it is right back to it falling on it's face. Also, there does seem to be a faint sound like boost is leaking when it falls on it's face, but I have checked and re-checked all hoses. I have dealt with this for so long that I am starting to lose my passion for the car and just want to get rid of it or get the problem fixed. This car is not fun to drive when it acts like this! Can someone, anyone please help?! I am at my wits end and do not know what to do. By the way, the car is on stock turbos at 75k miles, but they do not make any noise and do give full boost during those occasional periods.
Thanks in advance for any help you can provide.

Pat

S4gasm (LoTR)

see if the car holds pressure, when u do the pressure test, fill up the intake with air to the point where the pressure tester swells up and looks like its about to pop off, then disconnect the air line and plug that line with your thumb see if the sytem holds that air, if it doesn't then you still have a leak.

Use a hose or a stethoscope to see if you can locate where its making the hissing noise from.

HdiaS4

does your interior lights go off when the car looses power, or the cluster blinks?
Have you checked your MAF?

S4gasm (LoTR)

maf would be more consistent, thats been my experience.

Arcteryx::Stock Rods

and see. i would also talk to the mechanic who worked on your car and try to find a solution. why did you go with a samco hose kit when you're completely stock? i would check your maf sensor as well. could be clamps from the new hoses that were installed. try running an ecux log and posting here. good luck!

lazy n00b

after 3500rpm car stops boosting, ABS & traction control light, humming noise coming from front of the car. Ruptured WASTEGATE CONTROL LINE was the issue.

S4Dean

At what psi level did you pressure test? Maybe it wasn't high enough to expose the leak.

Jason Sowers(rs6's)

could he just unplug the maf then?

HdiaS4

leaks, i went to the next step.

S4gasm (LoTR)

sure but he doesn't have any problems at idle, chances are it will still fall on its face in boost.