I had to replace my passenger side axle yesterday so while it was at the shop I got the oil, spark plugs, and air filter changed. Im using the same oil I was using before, I swapped out a mann filter for an AFE Pro-dry, and the NGK plugs that were in there( not sure off hand) for the BKR6EQUP. Since I got the car back its been idling really rough and sometimes dropping bellow 500rpms while cold. Once it warms up its fine. The only thing really different is the spark plugs, I believe the ones that came out had 2 ground electrodes and the new ones have 4. I cant see how this could cause a problem.

Does anyone have any idea what might be wrong?

 

It was running fine the rest of today, i just went out and scanned it with the Vag-com. I got codes for random cylinder misfire on all 8. Once i cleared the codes it was acting up again but its fine now. IIRC this happened to me last time i changed the plugs, and did some major work. I looked the bay over and couldnt see anything that would cause a vac leak.

 

1 - are the plugs torqued properly? German cars are very sensitive to plug torque. You have to do it with a torque wrench, by feel is not good enough.
2 - are the coils seated properly? This is much less likely the problem but I got to throw it our for completeness.
3 - do you have the seperate ignition modules on top of the air box? If they are marginal, new plugs could cause a mis-fire.
4 - finally, yes, in some cases, 4 prong plugs could block the air/fuel mixture from seeing the spark properly, especially if you have #3 above. 4 prong plugs are great for longitivity at a cost of spark exposure to air/fuel mix (so, use them in your DD but not your race car).

#1 then #3 are my picks.

Good luck,

Bob

 

I dont think I have any ignition coils ontop of my airbox, atleast I didnt notice it. I will see if the problem persists and if it does ill remove a couple coils and test the torque. I will google it but if someone knows what the proper torque should be it would be appreciated.

On a side note the only other car Ive dealt with really is my "race car" and the plugs on that are totally flat with no protruding grounds at all. So i just went with site recommendations for these plugs.

 

Plugs get torqued to 22 ft-lbs. Nowadays, they are putting that on the side of the box the plugs come in.

Hope its that easy!

Bob

 

So the problem basically went away. So I assume its not the spark plugs itself. The car has been throwing the same codes since ive had it, (Fuel trim error :bank 1 and 2 running lean). Ive figured out through repeated clearing of the codes that it will misfire until these 2 codes are thrown and then it runs fine. Is it possible that the MAF is bad and causing the misfire?

 

If the MAF was bad enough to cause a misfire, it should send a code. Bank 1 and 2 lean is often an intake air leak between the MAF and the throttle body. Other sources of the lean code are a leaking EGR unit and leaking throttle body gaskets. None of these things generate a code, you just have to know what the usual suspects are..

 

Im not a mechanic but I had the same codes on my a6 3.0 after a coolant bottle change. I thought it was the maf also so I changed it. That was not the issue. Turns out it was a cracked vacuum hose coming from the back of the valve cover. The hose was made of plastic. I changed it with a small piece of heater hose and 2 aviation clamps. Very simple fix, never had an issue afterwards.

 

Sounds like a lean issue due to a vacuum leak. Start the engine and spray around with carb cleaner until the idle drops. Therein will be your issue.