I have a 2001 A4 quattro love it to death. But ive noticed that the engine sounds a little rough when sitting idle. Its it because of the gas I use, I use89 not 91 but maby the 91 octane will make the diffrence? Thanks in advance

 

1.8t or 2.8? use 91 or better. checked plugs, wires, maf? and cel codes?

 

2.8

 

throw some 91 in there and see what happens. get your car check through the obd2 port and see if you have any codes. check the spark plug wires, the spark plugs and make sure your maf is clean

 

I always use 91... I don't think 89 should be put in our cars...

 

The higher the octane thebetter. I always use 93 and up on my Audi but than again forced induction motors run more efficiently with high octane gas. With naturally aspirated motors it isn't as big of a deal but I would try some 91+. It could also be a number of other things like a vacuum leak or bad valve cover gasket.

 

I'd look into the plugs. My coppers went down to .038 from their original gap of .030. It took <10k miles and, once swapped for new ones, I noticed a difference in idle and response. You may not be using coppers but the same may be true even with platinums. If it's been a while, you may want to take a closer look at these.

 

Does it just sound rough? Can you describe the sound better?

Or is it running rough? Is the rpm jumping around and unstable? Does it run rough when driveing and not at idle?
Need some more info here, codes would be even better.