Shudder on 850-800rpm sometimes, sometimes not. Help? (chatterbox closed?)

[Majo]

2001 Audi B5 A4 2.8L
185xxx miles
5 speed

Sometimes, my car has a smooth idle, other times it has a mild idle, sometimes it has a ROUGH shudder and keeps bobbing up and down around 850-800rpm

I used a VAG-COM on for my CEL when the rough idle began, about a month ago, and i had a cylinder 2 misfire.

I waited a week for my next pay period, and by the time i was about to buy the parts, my CEL went away, and I had no CEL (disappeared by itself?)

Over the next few weeks, my CEL would appear and disappear on its own (perplexing me)

2 weeks ago, I use techron and fill it up while pumpin gas, my CEL goes away and the idle isnt apparent anymore. That lasts for a bit over a week, and this week the idle has returned.

Should I just get the coilpacks and save time? any suggestions?

[Bordom]

Check spark plug gap

Everything graciously mispelled by Android

[B5A4coastie]

The CEL can go away if the misfire only happened a few times (enough to log the problem with a CEL), but if it doesn't happen for X amount of time, the ECU will disregard the issue. Then when you get the misfire again, the CEL will come back. A few common issues are spark plug gap (cheapest and easiest), coil pack, and ICM.

First check the gap as Bordom suggested, if everything looks ok, then move the coil pack to another cylinder, if you start getting a misfire in the new cylinder then you know it's the coil pack.

[Majo]

Thank you very much!