Audi A4 Vacuum Hose Question
 

So I have a check engine light on, and it would appear the codes are basically telling me its a vacuum leak (and no, its not the gas cap).

So I found that on top of the intake manifold in the rear of the engine and on top of the throttle body there are several vacuum lines with different colors. There is a short blue and short brown cloth braided over rubber hose that go off to the driver side of the intake, and a black with tan spots hose and light green hose. All of the hoses are rubber with the braiding around them, but the green hose is hard plastic line after the rubber, and has a little rubber hose at the end of it after about 16" or so. This hose is just flopping around and isn't connected to anything!

Can anyone tell me where the green hose goes to in the circuit of vacuum hoses?

Should I just plug it off and see how the engine idles?

You might want to provide year and engine type of your car.
 

There are significant differences.

Oops... I meant to do that at the end. It is a 1996 Audi A4 Quattro 12V 2.8L V6. 116k miles... new timing chain, water pump, thermostat, pass side power steering rack and pinion, and various other updates.

Here's the vacuum line diagram
 

Maybe you could identify which line is disconnected.

The "EGR mod" shown on the drawing was to prevent the EGR valve activating during normal driving. A few people did this to prevent a recurring problem on the 12 valve V6 "EGR insufficient flow".

The braided hoses should be replaced. They could be 13 years old. Silicon hoses work great.

About 8 feet of hose would take care of it. The only tricky one is the "bomb (vacuum reservoir)" underneath the ignition coils.

Another common place for a leak is around the iCV.

This diagram works great! Thank you very much! I'm not in front of the car to know for sure at the moment, but I believe the line I'm talking about is in fact the one going to the vacuum resevoir. I remember the green lines were part of the "Y" connection, and it is probably the longest hose there. So the question is, how in the world do I get to that vacuum resevoir?

It also makes sense that the line that is disconnected is to the vacuum resevoir because I felt some differences in the brake pedal travel at idle and I just did some brake work with a new ABS pump and pads and bleeding.

So is reconnecting or re-running this line going to be a disaster? Would just rubber vacuum hoses work as replacements?

This help is much appreciated.

If the bomb is still good (not leaking) you should be OK .
 

It's awkward not impossible, regular rubber hose is fine if you can find the right ID hose. BMW dealers sell the braided hose by the foot, but it's $$.

Could you explain the EGR fix? My '96 would always set the "flow insufficient" code until I cleaned the clogged EGR and manifold passage. My understanding is that the temp sensor at the end of the passage has to get hot when the EGR valve is open, otherwise the fault code.

Where is the "bomb" vacuum reservoir?
 

So where is this stupid vacuum resevoir? Under the ignition coil? I have been looking around, but not sure where it is. Is it that canister that looks like a bloated insect with three ballooned out circles?

I'm Audi-ignorant, but mechanically inclined in fixing many other cars. So this is just getting interesting to me.

The EGR valve is controlled by a solenoid to give two modes of operation:

When the solenoid is off vacuum from the plenum opens the valve. So when intake vacuum reaches a certain level at around 3500 rpm the EGR valve opens and dumps exhaust into the intake for emission purposes.This happens all the time when driving.

The ECU can also turn on the solenoid and provide vacuum to open the valve. The ECU randomly tests the system for operation to make sure the emissions system is working. This is just a test and is not all the time.If this test fails it sets the CEL.

Unfortunately as the cars get older, blow by gas condense and block up the EGR port, which then needs to be cleaned.

The EGR mod allows the valve to open when the ECU tests the emissions but not allow the plenum vacuum to open it.

Thus the valve is open less often, this means potentially more power and that the EGR passage will block up less often.

However the EGR passage must still be unblocked for it to work.

Interesting indeed
 

The reservoir is right next to the coils, its a black plastic ball, the size of a grapefruit.

AudiMick, thanks so much for the diagram, and the EGR fix reminder. I was straining my eyes in the Bentley this morning trying to get the lines squared away on a A4 I just bought. There was no vacuum supplied at all to either the EGR, manifold change-over , or FPR. But the car was running OK, for 3 weeks, until this past friday when it became hard to start. Way too rich/flooding. still working this out.

Bruch