[V6-12v] Rough Idle

[Kent McLean]

David Torrey wrote:
> Well, I replaced all spark plug wires and the rough idle persists (wires had 180K miles on them).  Plugs are new. I checked vacuum connections and can't find any issues.  I have noticed that after the car sits for 8 hours there is no vacuum assist for the brakes until the engine runs for about 30 seconds.  Not sure if this maybe related?  Possibly check valve faulty in the vacuum line going to the brake booster? Could it be fuel injector seals leaking air or MAF sensor?  Any experiences appreciated.

Since plugs and wires are new, it might be one of the ignition coil packs dying. 
But I would think that would show up more at high revs rather than idle.

The ISV affects idle. Cleaning it is a cheap fix.
<http://www.audifans.com/kb/ISV_cleaning>
<http://www.12v.org/engine/index.php?section=cl&view=rear>

The oxygen sensor also impacts the idle; if it hasn't been replaced recently 
(<50K miles), then replace it.

-- 
Kent McLean
1990 V8 w/5-speed and other mods
1991 200 TQA #3, with mods
1999 A4 Avant, V6 Tiptronic
gone: '91 200 TQA x2, '94 100 S Avant, '89 200 TQ "Bad Puppy"