While I'm here...the check engine has been coming on and going off for about 6 months because its reading the secondary air flow is too low/sporadic. My mechanic just basically keeps telling me it's not worth it to worry about it at this point. I'm quite particular and just curious about anyone else's feelings about that...Supposedly it doesn't affect the car's overall performance but is only needed when the engine is started?

 

What motor? Common problem on the 2.7 is the diverter valves ruptering and leaking vacuum. 2.8's usually have issues with the vacuum lines running to the combi valves on the back of the heads. Neither common cause is expensive to fix. Possibly hard to diagnose if you dont know what your looking at. Kinda sounds like the situation here. The system isnt very complicated and shouldnt be too hard to diagnose. Your mechanic is right that the secondary air system only operates during cold start conditions and is only used to reduce emissions during that period.

 

thanks

 

I had a similar problem w ith my 96 wagon. Sound like a jet engine when cold. when car warms up, nothing. I had to have a cel cleared because of it. Low flow or something similar. Was told by a audi mech to run the car regularly on the highway at 70 mph to really heat things up and burn off the carbon that can build up.

Have not had the cel again.



Sorry mixed things up, the cel was for the erg valve. The advice was to clean out the valve.

 

the secondary air system injects air into the exhaust before the cat to creat a post combustion effect to heat up the cats as fast as possible so they can start doing their job.

 

The SAI only functions for a minute or so at startup. The SAI passages can get clogged with carbon over time and if the airflow is interrupted, it'll throw a CEL.
Not a big deal in terms of the function of your car, but a HUGE deal when trying to get your car to pass emissions inspection.
The last-of-the-aircooled 993 Porsches have been having this problem, and there is a method Porsche techs have been using to flush the SAI passages with techron and clear the passages enough to stop a Check Engine Light from being activated. Not sure if the Audi SAI is the same...I'm a lot more familiar with
the Porsche setup but hope that is of some help.

Oh, and the root cause of carbon and crap buildup in the SAI passages is - unfortunately - excessive valve-guide wear.