I bought a 99 A6 2.8L last week. Has 177XXX mi on the odometer. Today when I was driving all seemed fine. Hit a light and noticed I was idleing really rough and my tach was bouncing between 500 and 800RPM. And noticed a faint "chugging" here and there. It's running slightly sluggish and the exaust smells a little rich. Wondering if its a sensor, perhaps tps or o2. A vacuum hose came undone, or something more severe. I had to reconnect a hose on the back of the engine on the driver side next to my coolant overflow tank. Had to reconnect hose running from back of engine to a t-joint that looks to come from both sides of the engine. It seemed to help a little bit but is still having same issues just not as severe. Any ideas??

 

Are we talking about the breather hoses?
A picture speaks thousands of words. Snap a pic of what you reconnected if it isn't too much trouble.
Also, you need to specify if it's a non- or a quattro. The coolant tanks are located differently.
On a non-quattro, there are no hoses in the vicinity of the tank to speak of, beside the feed and return/overflow hoses themselves - which tank is located on the fender side.

Do you have by any chance the Check Engine Light on?

 

It is a quattro and it did pop the cel light with codes p1197p0411p0154 I have a pic but dont know how to upload it.

 

Codes are for driverside o2 sensor as well as the secondary air system malfunction. Anways, check the vacuum line going to the bank 2 combi valve vacuum solenoid. It looks like this and is located on the top of the engine towards the driverside rear, in front of the throttle body.



Just get a 5 foot section of vacuum hose from local supply store and replace sections as needed. It shouldn't cost you more than $10. Once you replace the vacuum lines and you still have the issue, then it maybe the front driver side o2 sensor. You should be able to find info on o2 sensor testing on this forum.

Good luck.

 

ok so was under the hood and heard an inconsistant hissing sound under the throttle body or intake. Like pssssssssss pss psss pssssss, is that normal or could it be a vacuum leak? I'm used to old cars. This is like going to china to me lol. I don't know how to test the hoses. They are a little stiff but I am afraid of messing anything up. I'm starting to run sluggish so i'm assuming its the o2 sensor. Idk tho

 

(Since you mentioned the exhaust smelling a little rich)
The EGR valve is also in that area... if the gasket aged and just disintegrated on you, you'll also get a hissing sound like you describe. Moreover, the EGR valve is vacuum actuated. If it has never been changed, then it vacuum hose may still be the brown-colored original one. If it is leaking, that could cause the EGR to malfunction and you'll experience exactly the rough, crappy idling and bucking on acceleration.
Just some food for thought.

 

Hmmmmm that makes sense cuz I noticed it smoking slightly and i'm sure that all of these would effect my fuel efficency too...where the hell do I even start? Lmao. I really appreciate the help guys.

 

Psss noise sounds like vacuum leak to me. If you grab the vacuum hose, then it will literally disintegrate in your hands. Just note the start point and the end point and replace the whole section. There is a vacuum diagram sticker under the hood as well.

 

BTW EGR Chefro is referring to is the same thing as the combi valve I am talking about. Tomato, Tomato...

 

This is how the EGR valve should look in your '99 Quattro:
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At least is worth checking and you have an idea what to look for if locating the solenoid Gaser mentioned.