I have a 1998 year A6 2.8 30V Quattro
I have a constant rough idle, the idle speed varies between 500 and 600rpm and causes a constant vibration through the whole car which spoils the whole solid build experience.
Took it into a dealer who ran diagnostic and quoted it as a variable valve timing unit and 1300 pounds to fix including labour there was no fault found on the diagnostic paperwork?, i did some research and audi dont do variable valve timing on this model/year.
took it to my local VAG specialist (Lions of leicester, great service) who laughed at the quote and ran same checks again no fault found but suggested that the ht leads were in need of replacement they also ran emissions test and said all ok and confirmed the variable valve nonsense.
since then i have replaced ht leads, plugs, ignition coil but its still the same, car seems to run fine with no (or not that ive noticed) loss of power still tops out at 147ish.
has anyone had this fault ? is it worth looking at fuel system?
any help greatly received

cheers

 

I would check the vaccume hoses, the idle air control valve and trottle body alighnment. I wouldn't believe it is in the fuel system due to the fact there is no codes and the top speed seems fine and the power seems fine you say.

 

Thanks for the help, i will check all those. it may be down on power but not significantly.

cheers

DazA6

 

i had a rough idle and after i did a full tune up, i.e ; air filter, plugs, coils, oil change and fuel filter the cars idle returned to normal, a car in need of a tune up wont always throw a code.

 

It might be worth your while also to go through the engine bay and clean your electrical connectors with a contact cleaner (ProGold is the best I've used, but it's very costly - still, it's worth it). Specifically I'd make sure to clean the mass airflow sensor connector, as well as the idle air control, coolant temp, and (I'm not sure if these cars have it or not, but probably) a fuel temp sensor as well. Any of those could have an effect on the idle quality of the car, and if they have corrosion on the contacts, cleaning them up and ensuring the ECU is getting an accurate signal can help to smooth things out. I do this from time to time on my cars - cleaning any and all connectors that I can reach - and it can make a nice difference if something is corroded, and if not, it's good preventive maintenance, all the more so considering that it's easy, cheap, and doesn't take all that long to do.

 

Clean the throttle body. If that doesnt work i would suggest an engine decarb. Sometimes carbon builds up on the valves of the 2.8 and causes the engine to run rough. Also check for vacuum leaks.