Tech Article Title Author Date
S4 Throttle Body Hose Replacement Don Pavlik 2000

S4 Throttle Body Hose:
Thar she blows!!

If you've noticed that your S4 feels down on power, surges under heavy load/throttle or has the sound of rushing air from under the hood "that you never noticed before" there's a chance you have a ruptured throttle body intake hose.  My S4, with a mere 6,100 miles on the clock, fell victim to this failure.  The thing that amazes me is that it ruptured under the clamp then blew out allowing my thrust-producing boost to vent into the wilderness.  Graphics intensive page... sorry about the wait.

Ruptured intake hose: the tear was nearly 1-3/4" long!

For about a week the car was surging under heavy load and feeling generally "unfrisky" compared to normal. "Bad gas" I postulated although I was planning to hook up my scanner and check for engine codes despite that the CE light was not glowing. Then, while heading out to lunch one fine day the car started running like a total dog. If I leaned on the throttle I could hear air rushing under the hood.  I knew immediately an intake hose somewhere had failed or blown off.  I had read a few things online about a weak hose--my gut told me that was my problem.  A quick inspection confirmed the hose was ruptured.  Damn.

I stopped at the dealer.  I'd heard that availability was a problem with this hose so I checked with the parts department before admitting my baby to the service department--the part was on intergalactic backorder.  None in the US and not available for 4-6 weeks due to a part change I was told. OH MAN!!  I made a few phone calls... luckily, APR had one in stock.  I bought one from them and installed it myself.  I can see the email already... why did you buy the part yourself when the car is obviously under warranty?  Quite frankly, for a $7.80 it wasn't worth the hassle waiting for the dealer to dig up the part and the pain of being without my S4 when one was readily available to me.  Yes, I suppose I should push to be reimbursed for the part.

Install time:  about 20 minutes including taking pictures.

The boot has been replaced by a new part that sells for $11.80 instead of $7.80.  I have both the old and new part number boots.  There is no visible difference between the two... apparently, the difference is in the rubber compound.  

Btw, replacing the hose did not reduce the low rpm turbo "whirring" noise some have asked me about.  The hose was not contributing to this normal noise.

Revised 

Audi has released a technical service bulletin regarding the throttle body boot failures.  The revision uses the 356T boot and redesigned clamps.  Complete info may be found at http://tech.vw.com/audi/newtech.htm.  See bulletin # 01-00-04. Adobe Acrobat reader is required to view the service bulletins.  The bulletin calls for 4 new clamps.  So far I've only replaced the main clamp on the throttle body opening--the others were not yet available.

Revised part numbers

Boot original part #

078-133-356L

Boot new part #

078-133-356T

New main clamp#

078-133-343

Original clamp contributes to failure
click to enlarge

  • Sharp points on the original clamp cut into the boot then the boot rips under boost pressure

  • The sharp points cut into the rubber.  Hard to see in this picture but, in person, the rubber is indented.  The light spot just to the right of the point in the tear is where the rubber bulged into the indention on the back of the clamp.

  • The new revised clamp is smooth on the inside.  Hopefully, this will prevent injury to the revised replacement boot.

The two failures below were replaced without using the new clamps (revised clamps were not announced at the time).  So, simply replacing the boot is only 1/2 the battle.

Revised Boot Failure!

  • The revised "T" suffix boot is not immune to failure.  Pictured at the left is a revised boot that ruptured under the main clamp on LCPs S4 after a few short months of service.
  • Note: This failure was with the old style clamp
  • My 2nd boot failed at 15,500 miles after 9,400 miles of service.  I was entering the freeway, shifted into 2nd gear and a few seconds later I  felt the power drop off and heard the tell-tale whooshing sound of a ruptured throttle boot.  Damn. 
  • Note: This failure was with the old style clamp
  • Every boot failure I've seen fails the same way.  The lip on the boot fits into a mating groove on the throttle body.  The boot tears at the lip edge. This begins when the boot is cut by the clamp on the outside.


Where the weakling lives

Remove the "V6 Biturbo" cover to discover the throttle body and the throttle boot lurking within
(dipstick extraction not required)

 

To replace the hose:

  • Remove the two philips screws that secure the snorkel. 
  • Pull the airbox end of the snorkel straight up.  A small clip holds it in place.
  • Watch that the clip does not pop off and drop into the airbox or the dark recesses of the engine bay.  
  • Remove the Biturbo cover (if still in place).  The dipstick need not be removed. 
  • Loosen the two 10mm bolts that secure intercooler pipes.  I didn't remove the bolts... I just backed them out a few turns.
  • If you don't loosen the bolts you risk breaking the pipes as you try to extract the old boot!
  • Remove 2 allen screws (5mm). These were very tight.
  • Remove 2 sensor nuts (8mm), watch out for those teeny-tiny washers... if you drop them chances are they will probably be lost forever in the black hole that is the engine bay.
  • Disconnect the sensor connector.
  • Loosen 2 intercooler pipe clamps (7mm or a screwdriver).
  • The sensor in this picture is the biggest pain of the whole operation... getting it into the new boot can be a challenge.
  • With the intercooler clamps out of the way, gently pull the pipes out of the boot. (Did you loosen the intercooler pipe bolts already?).
  • The rubber boots on the other end of the pipes allow enough movement for the extraction.
  • Loosen the throttle body hose clamp and wiggle the boot out.
  • Remember to hold your mouth "just so".
  • Transplant the sensor to the new boot (replace the annoying factory clamp).  I used a clamp with a max size of 7/8" although it was just barely big enough. A 1" clamp would have been a better choice but it was too wide to fit properly.  Note the orientation of the sensor.  I found it easier to put one of the 8mm nuts on the sensor bracket and secure it to keep it from getting in the way while coaxing the (obstinate) sensor back into the boot.
  • The body of the clamp has little holes in it. One of the holes has a little finger holding the position (kinda like the holes on a belt you would wear with your pants). Pop up the end of the clamp to release it off the little finger.
  • Generic clamp pictured
  • Note all the dirt that fell into the throttle body area.  Clean up this grit before you re-assemble!
  • Be careful not to apply pressure to the throttle valve plate if you have to clean up debris.  The throttle plate is motor driven and the drive assembly can be easily damaged if you move the plate.
  • Make sure the boot and throttle body surfaces are free of any oil or lubricants.  Oil allows the boot to move and my contribute to future failures. 
  • Put it all back together.
  • Enjoy S4 power once again.



Terms of Use Privacy Policy| Copyright © 1996-2012 by AudiWorld. All rights reserved.