Edd W

If you have a mis-match between throttle position and MAF reading then it suggests a possible air leak between the two.

If you start it up with the maf pulled away from the air box then breifly place you hand over the maf inlet you should get a fairly strong suction with little in the way of leaks, even at idle.

Have you cleaned the MAF sensor?

is the air filter good and nothing odd blocking the air inlet tract?

The one way valve you have found probably is OK - I do not know that exact valve as I have never had any probs with air leaks or pipe failures of any kind, but they often are not a perfect seal. The Vacuum will be re-created by the engine within the first few seconds of running anyway, providing there are no leaks and the valve is at least opening the correct way.

What engine is it - I guess 2.8 or 4.2 as the 2.7t does not have the same vacuum system.

When you return to the car after a while, is there still vacuum avalable for the brake servo?

tester123

>>If you have a mis-match between throttle position and MAF reading then it suggests a possible air leak between the two.

So wouldn't this mean a leak in the intake plumbing -so to speak?


>>If you start it up with the maf pulled away from the air box then breifly place you hand over the maf inlet you should get a fairly strong suction with little in the way of leaks, even at idle.

This is the case. The suction is good. So I am thinking no leaks in Air Intake starting from Inlet to engine intake manifold

>>Have you cleaned the MAF sensor?
I have not done this. What would be correct way of doing it? (i.e. cleaner to use, procedure)

>>is the air filter good and nothing odd blocking the air inlet tract?
This checks out ok. No blockage whatsoever.


>>The one way valve you have found probably is OK - I do not know that exact valve as I have never had any probs with air leaks or pipe failures of any kind, but they often are not a perfect seal. The Vacuum will be re-created by the engine within the first few seconds of running anyway, providing there are no leaks and the valve is at least opening the correct way.

When I unplug this after few mins of engine idle and shut off, there is vacuum as air seeps back in. So, I am guessing it is good.


>>What engine is it - I guess 2.8 or 4.2 as the 2.7t does not have the same vacuum system.

I did miss mentioning this didn't I? It is 4.2

>>When you return to the car after a while, is there still vacuum avalable for the brake servo?

Brakes work fine. I don't know much about brake servo yet. How do I go about checking this point?

And, thanks for taking time to reply!

Kris Hansen

I still think either MAF or MAF wiring.. Or, Throttle position sensor.

tester123

I think I am with you on this. Will clean the MAF and see if that stops these codes... One good news is that I generated the readiness code through the procedure and "Luckily" the CEL didn't come on and I passed the inspection finally!!!

Now, on to figuring out what the heck is causing this.

Obviously this is intermittent so, it's going to be a pain in the neck to find out. Let's see.


Also, can you suggest a good place to buy OEM / OEM equivalent parts for Audi? I know there are so many places there but I just can't trust them when they are quoting me a gasket for $9.95 when the dealer item costs $90+.. some thing is wrong with that picture.

Kris Hansen

I use my local euro-specialist, or Axis Motorsport(www.axismotorsport.com) when my guy can't get a certain thing... send them an email, they should be able to help you out.

tester123

Thank you. I'll give them a try

tester123

I have searched extensively on this and other forums to trace this problem to its final end. So, I'll keep updating this thread with my findings / resolution so that someone who might have similar issue(s) will find a solution quickly.

Update:

I cleaned the heck out of the MAF sensor using Alcohol. Just poured some in a ziplock bag and shook it vigorously by holding the connector's end and dried with dry cool air from compressor (from a distance. The idea is to dry it not force everything out of it - also if you are doing this, get rid of sand/dirt from the connector with a paint brush or etc. so that dirt doesn't go into the sensor when dipped in alcohol). Took it for a test spin and no codes showed up so far. Will keep updating.

tester123

As promised, I am here to update my findings (although, the thread is couple years old...)

Anyway, the issue regarding incorrect flow is related to the Evap Purge valve or N80. It was misleading because the resistance readings on the valve and voltage readings from wires are all good. There is no residue or visible debris in the valve and I went ahead and replaced all vacuum lines and still, the issue remained. Finally, after replacing the N80 valve with new one, the issue is resolved.

Here is a check-list for someone in the same boat:

(A brief overview on system operation. When the engine turns on, the "leak detection" pump -located in rear wheel well- runs to pressurize the gas tank and evap canister to some 15mbar etc. and the diaphragm on top of the pump is engaged. Now, if there is a leak, the pressure drops the diaphragm and throws the code. In normal operation, the system runs and ensures no leakage and then periodically opens the N80 or Evap purge valve -located near the air intake hose near the MAF sensor- and dumps the fuel vapors into engine to burn up.)

1) Check all vacuum lines - including the ones going to leak detection pump.

2) Ensure all fittings are tight and no leakage - pressure loss will fail the diagnostic and throw the code.

3) Check N80 valve - bench test it for coil readings and vacuum test for proper operation.

4) Check fuses and power on all related wires. (Leak detection pump uses the same fuse as fuel pump - not totally sure, so check it against a manual)

5) Check Evap hoses (evap canister is in the spare wheel well under the trunk)

6) Using Vag-Com, run tests on Engine > Basic Settings > groups 070 - Evap Purge valve test (N80) and 071 - Leak detection diagnostic test. (Follow the manual on operating temp & conditions)

7) Last but not least, make sure the simplest thing, the Gas Cap's seal is in good condition. It is a good thing to replace if you haven't changed the cap... You can order just the gasket instead of the whole cap (unless of course, the cap is damaged).