I have a 99 Formula and it has a rough idle also. When I put the clutch in as I'm coming to a stop the revs like to hang up for a few seconds too. Up around 1200 then eventually drop to around 700 to 800.
Did an H/C swap over the winter and at that time put in new plugs and wires. Had the TB ported and polished. Had the car tuned with LS1 edit. Car still idles rough. The car has just over 40K on the clock. Maybe that is just the way these cars are??

 

Another '00 rough idler here

 

my formula has a rough idle. When I sit at a light it will shake the whole front end a little. My car is an A4 and its got almost 81k miles. changing plugs wires, and getting my TB P&P next week. I;ll let you know if that helps the situation for me.

 

Yet another rough idling 2000 here. After we installed my Procharger and got it tuned when sitting at a stoplight it'll be just fine and then "hiccup". It's pretty random when it does it and so far it has never stalled completely out but it has come close. I'm just wondering if increasing the idle speed slightly will help smooth it out a little? It's been doing it for about 9 months now.

 

i had rough idle too..after the fuel lines were replaced....nomo rough idle...small specks of rust were getting into the injectors causing the rough idle.

 

Wow ... old thread ... I was going to post on it and found out I already did (twice). Anyway, in my case, it's a year later and in the meantime I've done plugs, fuel filter, and air filter and my idle is still kinda rough. Strangely, some days are worse than others for no apparent reason.

 

After my header install i had a rough idle. Then i found out one of my spark plug wires werent connected and i was running on 7 out of 8. LOL

 

i'd say pcv system or tuning