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Fixing Audi A4 Common Vacuum Leaks
 
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Pelican Technical Article:

Fixing Audi A4 Common Vacuum Leaks

Steve Vernon

Time:

1-6 hours

Tab:

$15 to $200

Talent:

****

Tools:

Pliers, screwdriver, sharp knife

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

New hoses and valves

Hot Tip:

Use caution working with old hoses

Performance Gain:

Car runs like normal again

Complementary Modification:

Clean MAF sensor

All modern cars use the vacuum created by the induction system and the motor to run various systems and components on the vehicle. The Audi A4 is not different in this regard and uses vacuum to assist in the EGR (exhaust gas recirculation) system as well as the intake system. The EGR is part of the efforts used to recirculate unburnt gases from the motor back into the combustion chamber to be burnt and result in a cleaner running engine. Vacuum is also used to control the amount of air entering the combustion chamber. This volume of air is carefully metered and the information is used to determine the amount of fuel added to the air and the timing of the spark to determine the maximum function from the engine; this will result in the best possible miles per gasoline while producing the least amount of harmful emissions.

Any sort of leak or unmetered air caused by a leaking, cracked or split hose, hose clamp or broken fitting can result in a poor running engine, failure to pass a SMOG test or a motor that will not run at all. Don't forget to check places where vacuum leaks may not be as obvious, such as the oil filler cap and the dipstick.

This article will go over the location and fittings of the EGR, EVAP, ventilation and vacuum hoses on the motor. Each hose, fitting and clamp should be inspected. Hoses should be soft and pliable. Any dryness, rips, cracks or bulges in a hose means it is well past time to replace it.

There are a series of hoses and valves making up the vacuum and emission systems on the vehicle.
Figure 1

There are a series of hoses and valves making up the vacuum and emission systems on the vehicle. The main areas to check are above the intake air cleaner (red arrow), to the right side of the rear of the engine cover (yellow arrow), and to the rear of the intake manifold (green arrow) and the intake manifold itself (blue arrow).

The area to the rear of the intake air box contains the EVAP valve (red arrow) and lines (yellow arrow).
Figure 2

The area to the rear of the intake air box contains the EVAP valve (red arrow) and lines (yellow arrow). If the EVAP valve is throwing an error code, it is best to just replace it. The lines should be checked for condition and replaced as needed. The hose clamps used from the factory need a special tool to reuse. Most people just pry the clamp off with a screwdriver and replace the clamp with a standard hose clamp.

In front of and below the intake air box is the secondary air pump (red arrow).
Figure 3

In front of and below the intake air box is the secondary air pump (red arrow). There are two plastic lines that will split when cracked.

The secondary air pumps intake line connects to the air box (red arrow).
Figure 4

The secondary air pumps intake line connects to the air box (red arrow). The output line connects to the combi-valve (yellow arrow).

At the rear of the engine you will find the combi-valve (red arrow) and a series of hoses and valves for the EGR system (yellow arrow).
Figure 5

At the rear of the engine you will find the combi-valve (red arrow) and a series of hoses and valves for the EGR system (yellow arrow). The lines should be checked for condition and replaced as needed. The hose clamps used from the factory need a special tool to reuse. Most people just pry the clamp off with a screwdriver and replace the clamp with a standard hose clamp.

The intake manifold has a series of vacuum and EGR hoses attached to it.
Figure 6

The intake manifold has a series of vacuum and EGR hoses attached to it. On the rear is a line that connects to the EGR system. Like most of the hoses, it came from the factory with a clamp that is very difficult to reuse (red arrow). If you are ordering new hoses, you should also be getting new clamps to be on the safe side.

There is a vacuum line on the right side of the manifold (red arrow).
Figure 7

There is a vacuum line on the right side of the manifold (red arrow). This hose has been worked on before and already had the clamp replaced.

While the gasket that seals the crankcase ventilation valve is not as critical as a fuel seal, it is always a good idea to replace it (red arrow).
Figure 8

While the gasket that seals the crankcase ventilation valve is not as critical as a fuel seal, it is always a good idea to replace it (red arrow). These gaskets get old and dry up and leak over time.

With the intake manifold removed, you can see the crankcase breather hose (red arrow) and the turbocharger recirculating valve (yellow arrow) and the secondary air injector solenoid (green arrow).
Figure 9

With the intake manifold removed, you can see the crankcase breather hose (red arrow) and the turbocharger recirculating valve (yellow arrow) and the secondary air injector solenoid (green arrow). The lines should be checked for condition and replaced as needed. The hose clamps used from the factory need a special tool to reuse. Most people just pry the clamp off with a screwdriver and replace the clamp with a standard hose clamp. These hoses and valves are all mounted below the intake manifold and cannot be serviced without first removing the manifold.

While the clamp that seals the crankcase ventilation valve is not as critical as a fuel seal, it is always a good idea to replace it (red arrow).
Figure 10

While the clamp that seals the crankcase ventilation valve is not as critical as a fuel seal, it is always a good idea to replace it (red arrow). This hose gets old and will dry up and leak over time.

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Comments and Suggestions:
Pez Comments: Hi Guys, From my 2001 Audi A4 B6.

Looks like I need a new hose and wondered if you recognised this? It's the small braided hose that you can see in the photo through the manifold. The one that forks to the right with a silver collar. The other end is not attached to anything at the moment! Any help identifying what it is and what it does or is supposed to do would be greatly appreciated. Thanks a lot.
October 17, 2016
  Followup from the Pelican Staff: See if this diagram helps. I found it in the forums. You can replace the hose with a new section of braided vacuum hose.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.

- Nick at Pelican Parts
Blandy Comments: Hi Guys, where does the front vacuum hose on the intake manifold connect to? I have just had the rocker gasket replaced and the mechanic has left the hose off. He couldn't find where it connected to from the manifold! My car is a A4 1.8TQ B5 1997. Has 105,000 klms on it.
July 25, 2016
  Followup from the Pelican Staff: it could be the hose for the secondary air or the fuel pressure regulator. Check the hose diagram on the emission sticker under the hood. - Nick at Pelican Parts  
a REAL tech Comments: Im glad u appreciate it, I wasn't trying to b a jerk just trying to get the correct info out there for people that DON'T know ok cool
August 14, 2015
  Followup from the Pelican Staff: NAH! I love when you guys chime in and help us improve things around here. Can't do it alone. - Nick at Pelican Parts  
a REAL tech Comments: its exhaust gas recirculation not electronic gas recirculation
August 5, 2015
  Followup from the Pelican Staff: CORRECT! Thanks for catching the typo. We appreciate it. I will have the article updated.- Nick at Pelican Parts  

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