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Having owned my RS4 for 3 months i knew it wasn't quite pulling as it should, when it hit 5500 rpm it just didn't want to rev and felt like it was holding back all the way to the red line,i was disappointed with the performance and wondered what everyone was going on about so i decided to check for vacuum leaks, i isolated the air filter power flap from the vacuum system and placed a boost gauge on the vacuum line and rigged it up so i could check the vacuum level whilst driving, and wow what a difference when it hits 5500 rpm it just pulls like a train its totally different even the induction noise is different, i located the fault to a leaking air filter power flap solenoid valve which also meant the IM flaps would not have been working properly so instead of replacing the valve i have ordered parts from demon tweaks for a CAF hopefully it will make even more of a difference.

If the manifold flaps were not working then you get a code thrown pretty quick. The ecu is pretty sensitive to what the flaps should and actually are reading.

Iirc if the there are circumstances where the ecu sees the vacuum leak, doesn't throw a code but limits the ignition timing resulting in dramatic power loss.

When you took the vac line off did you get a 'psssssss' noise?

Did you get an EPC light?

just had similar loss of 'kick' at over 4000 and diagnosis was new air filter cap and solenoid needed....appears to be under warranty

I had the EXACT same problem. Disappointing power especially after 5.5k. There was a crack in the air box power flap solenoid. I was getting P2015 code on the very odd occasion and exhaust flaps were rattling when car was stareted cold during catalyst warmup. Manifold and air box flaps failed VCDS output test but exhaust flaps were working which means there was some vacuum in the system.

Got solenoid replaced and all good in the world again. Much improved overall feel to power delivery.

Exhaust flaps have their own vacuum reservoir.

neckarsulm wrote:Did you get an EPC light?

No I did not get an EPC light, just no top end power, can't wait to do the CAF now.

adsgreen wrote:If the manifold flaps were not working then you get a code thrown pretty quick. The ecu is pretty sensitive to what the flaps should and actually are reading.

Iirc if the there are circumstances where the ecu sees the vacuum leak, doesn't throw a code but limits the ignition timing resulting in dramatic power loss.

When you took the vac line off did you get a 'psssssss' noise?

Yes there was a vacuum their when the car was running but nor enough as it was leaking, it also would not hold the vacuum with the engine off.

HEo2TEC wrote:

neckarsulm wrote:Did you get an EPC light?

No I did not get an EPC light, just no top end power, can't wait to do the CAF now.

I've just looked at the kit I think you have - where do you plan on putting the air intake? There's not a lot of room at the front and most specialists fit a caf by removing one of the auxiliary radiators in the bumper.

Yeah that's the common thing - a small leak may be overcome with the large amount of vacuum the engine can produce at low throttle settings. What's probably happening is that theres enough vacuum to actuate the manifold flaps at 3k rpm so keeps the ecu happy but at high throttle openings the vacuum leaks out and the manifold flaps start to move back to tumble slow enough not to trip the ecu but fast enough to starve the engine of oxygen.

Quick fix is to plug the throttle box power flap vacuum line.

adsgreen wrote:

HEo2TEC wrote:

neckarsulm wrote:Did you get an EPC light?

No I did not get an EPC light, just no top end power, can't wait to do the CAF now.

I've just looked at the kit I think you have - where do you plan on putting the air intake? There's not a lot of room at the front and most specialists fit a caf by removing one of the auxiliary radiators in the bumper.

The CAF kit I have is the same that MRC fit, I have heard that you have to remove the aux rad and secondary air injection pump I'm hoping it can be done by just removing the aux rad as I'm not getting it remapped just yet, I should get an even better top end when I've done the CAF as my air filter power flap is not working.

Hi Guys:
Just thought I'd throw in my experiences with vacuum problems on B7 RS4. At about 180,000 km, did a carbon clean, installed new Hitachi injectors and JHM intake spacers. Per JHM advice removed flow dividers. Car wasn't running great, and had a hard time getting to 8250 red line. Eventually threw a 4" vacuum gauge on my windshield and started driving. Only about 11 in Hg vacuum. The exhaust flaps had been disconnected but when I hit the sport button, vacuum decreased more. Vacuum leak in exhaust flap actuator. So I disconnected the vacuum upstream of the actuator and plugged the line. I logged the intake flap position while it was running the low vacuum and determined that the flaps would go open at 4500 ish rpm and then slip closed again because they'd used up all the available vacuum. Strangely enough, no fault code on flap position. I dug into it further and sprayed the intake of the crankcase oil separator and vacuum jet pump. Went for a drive and voila, vacuum up to 30 in Hg. Intake flaps go open and stay open! I purchased a new triple sep and jet pump but have yet to install them (not sure my hands are small enough or my fingers long enough for that job). So any time it feels a bit sluggish, I spray the inlet of both with some brake clean until I get around to installing new parts. Bottom line is I'd suggest the vacuum gauge as a pretty economical way to check engine performance. So performance seems pretty good but I'm getting 0172 and 0175 fault codes - , rich mixture banks 1 and 2. Does anyone that has had these fault codes have advice on how to prevent these two fault codes or troubleshoot?
BT

It is worth reading SSP 377 before trying to diagnose issues.
This gives all the details of the vacuum system on the RS4 engine and how it operates.
It may save you a lot of time.