Really not sure what to think. At first I just figured that one the the turbo's is on its way out, but the more and more I drive it I tend to think that this isn't the case. I haven't had time to put it on the lift and check it out, but here is what it is doing....

When I first start the car I have a nice clean start up no unusual noises, no rough idle, no smoke(white/black). While the car is cold it runs perfectly, boosts 9-10psi (stock tuning). When the car reaches operating temperature this is where things get fuzzy. The boost reduces to 5psi and in lower gears with low road/engine noise I can "sometimes" hear a flutter coming from one of the turbos I think. I have 2 codes that have been up for a long time, one is for an evap vent and the other is for a rear o2 on bank 2. The car ran fine for months with those codes up so I don't think this has anything to do with what is going on but I figured I'd just throw it out there.

I'm now starting to think that maybe its a wastegate/n-75 valve issue? But I could have been right in my first assumption that the turbo is just on its way out and it makes a nice seal until intake temps get high enough to heat up the damaged seal and and loose its viability.

Tell me what you think? I won't call you an idiot for trying to help so please....

 

could be a bad dv. are you on stockies? i'm also with you on the n75 valve. i hope its not a turbo. good luck. . i hope this helps.

p.s. once i had a loose inlet and the same thing happened with the psi at temp. i was later told i had been put into limp mode, due to the loose inlet, which caused the low psi. doubt thats your issue though. this was before i started working n my own car so i dont know how valid this statement was considering the repair shop.

 

thanks for the input, I will put her on ramps and scope the inlets and try to wiggle the actuators in the AM, I'm using APR R1 DV's they are about 5k miles old, but if it was just a bad DV I would be a lot happier then if it was one of the turbo's obviously. Thanks again.

 

Sounds like you're going to limp mode, Id do a boost pressure check on the car, pressurize the system and listen for leaks. No CEL's?

 

I just bought a 2000 S4 and found this thread because of the way you described the "fluttering" sound your turbo is making. My car runs perfectly w/no CEL but when I'm driving next to a fence or retaining wall, at low rpm and give it just enough throttle to hear the turbos spool up, I can hear a simmilar fluttering sound. I have removed/tested the dv's and am confident they are not the problem (I've been through that before) and like I said, the car runs pefrectly but it is just boggling my mind what this sound could be. It sounds like possibly a tiny exhaust manifold or gasket leak but I just can't put my finger on it. I just hoped maybe someone would offer up an idea that might help us both..

 

Rowe have you checked your hoses for tears? specifically the throttle body boot?

 

rowe: i have a very similar problem, spose i too should check the throttle body boot. does anyone know if the throttle body boot from a 2001 will fit a 2000?

 

Thanks for the tid-bit. I will go check the throttle body boot as I have heard they are a problem area. I know for sure that some of my vacuum hoses are in bad shape so that will be one thing I do. I appreciate the idea though and will check it out.

 

So I've been doing some research, does the S4 have the K03 turbo stock? Is it the same turbo that the 1.8T has?