Occasional Rough Idle and Code

B6/7 S4/RS4
#1

Noticed my car has a slight rough idle lately (+/- 30 rpm) and occasionally when I put the clutch in the idle drops to around 600 rpm before recovering back to 800 or so. A couple of months ago I picked up a P0441 code a couple of times, but it cleared itself out after a few drive cycles. Think it set and then cleared three times total.

If it’s not setting now, I’m not sure how important this is, but will an issue with the EVAP system screw with my fuel economy drastically? A basic Google search makes me think it might be the N80 valve, but I think it was an AZ link so I take it with a grain of salt.

#2

There is a code look up section in the tech section on this site. The evap system shouldn’t effect the fuel in a negative way. That is just a purge valve. How old is your fuel filter that can cause issues with low rpm idle issues.

#3

I would check for a vacuum leak. Around the intake manifold and make sure that the MAF boot is on correctly.

#4

Vac leaks always cause issues def check this as well

#5

First off, sorry for not realizing there was a code look up section. Rookie move on my part.

Not sure on how old the fuel filter is, I haven’t changed it in the 20k miles or so I’ve had the car. I’ll look into doing that myself if it’s not that difficult. How would I find a vacuum leak?

#6

Don’t worry about the code look up I was just passing that on so you knew. Look in the tech section there is also a DIY for changing your fuel filter. For a vac check you can check vag com to see the fuel trims. Do you have a vag com.

#7

The easiest way to look for a vacuum leak is to have the engine running at idle and spray starter fluid around the engine to see if the engine revs up. I would start by spraying around the intake manifold and throttle body, then the pcv valve and lines, and next the MAF.

You can also look at the long term fuel trims like Justin mentioned. Don’t clear the codes before looking because that will reset the long term fuel trims to zero. Go into channel 32 and let us know what the values are. Values 1 and 3 are for long term fuel trims at idle and values 2 and 4 are for long term fuel trims with the throttle opened at all.

#8

I don’t have VAG-Com, but I do have Torque on my phone and can read out basic stuff. I’m know I’ve seen fuel trim stuff in there before, I’ll have to check later to see if it includes long term stuff.

#9

Great advice Jimmy. I would start with a can of starting fluid and spray it around the back of the motor by the throttle body and then by the intake where the heads meet the intake.

#10

Already been said but yeah I would check the basics first. clean the MAF, check for obvious leaks.

I actually bought this bad boy for testing for vac leaks. You can usually find known good vac readings online on forums and what not. Then compare yours.
http://www.amazon.com/gp/product/B00GYTR9OQ/ref=s9_simh_gw_p422_d0_i3?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=desktop-2&pf_rd_r=16PX4X34TTEC2SHF39A8&pf_rd_t=36701&pf_rd_p=1935661402&pf_rd_i=desktop