I own a 2001 A6 2.7T, and I have been expiriencing intermittent rough idles. Temperature does seem to play some role (worse when cold), but it is inconsitent. I also have had a 2MPG drop in fuel efficiency the last 2-4 mos. So my question is could it be an O2 sensor, and idle sensor, or some other sensor without triping the check engine light??? Techs please help. Thanks.

 

Check your coolant temp sensor, I think it's in the rad.. known to cause a drop in mileage, as the ECU gives the engine more fuel thinking it's not warmed up yet.

 

if you got a CEL pull the codes and then report back to us for a more thorough look into solutions. pepboys should still pull thekm for free.

 

Pep boys should be able to give you the codes, now if you're going to keep the car for a while, get a VAG-com, great for diagnozing faults and/or modding our Audis, and finding faulty O2 sensors.
VAG-COM is your friend.

 

can someone help me i am getting a check engine light and i have an after market radio audi says i need original inorder to get the codes does and one know the relay to bypass this?

 

I'm no expert, but I think it could have something to do with the air injection system. From what I understand, there's a pump that sucks air into the system to control how rich the mixture of air and gas is, particularly at various temperatures. If you have a cracked hose (or pipe - I think they may be plastic pipes) you'll get an air leak and the system will become inefficient.

As a result, you'll get a rough idle because it will have trouble controlling the richness of the air/gas mixture.

Hopefully someone who knows better than I do will come along and correct me if I'm wrong.

 

You dont need the original radio, but you will need to pull your radio and do some rewiring. Whoever installed the radio either shorted or powered the data bus wire on the radio causing the whole system to go down making the scan tool not comunicate. Sometimes just pulling the radio fuse will work, but sometimes a rewire of the radio is needed.