2.6 V6 wont idle, hunting severely very strange.

[stuttgartmetal]

Here's a good one.
1997 2.6 V6 80 Cabriolet manual.
Usually runs perfect.
30MPG and fast.
I decided yesterday to change the stereo and clean the car.
Took the Sony CD player and multidisc changer out of the boot.
Fitted a Becker fine.
Took the car out, had trouble starting on the way back, but started and ran fine.
Spent the day T cutting and waxing the car.
Went to start it about 5, wouldn't start.
Plugged a charger onto the battery.
2 hours later the car started first time, without touching the throttle the revs rose to about 3000 rpm.
After a few moments [ about 2 minutes, I let it do its own thing] the revs slowed to 1400 and now it hunts really erratically.
Like room, room ,room, room, 1400 rpm.
It feels like either a stuck on cold start injector, or anti-stall valve.
Very difficult to drive, as it wants to get away from you on idle.
I took it for a caning down to the M25 last night. All the normal power is there, but just wont idle.
Its like someones intermittently pressing the throttle.
Thats why I think a cold start injector is pushing fuel in.
Any clues anyone ?

[stuttgartmetal]

WTF, its fixed itself, Eh?
Magic elves.

[tuscy]

Had the same thing on a 2.8V6 a few years back. I think it was the throttle bypass valve (probably the same as the anti-stall valve) playing up. Used to come and go, had the valve changed and problem was sorted.

[stuttgartmetal]

Yup, that sounds about right.
Where is it on the engine, and how much to buy one ?

[tuscy]

I had it fixed by Audi, I think the part was about £150, don't think there was much labour involved.

[Daggerpie]

Yep, sounds like throttle bypass valve, i had similar on my 94 2.8 coupe. My local Audi indy sorted it for about £140.00 if i remember correctly..

[istoo]

the item in question will be the idle stablisation valve, little pot over from the MAF (or behind the air box if you have the 2.6) These get bunged up and sticky over a period of time.

http://www.12v.org/maintenance/repairs/isv.php

my 80 quattro used to wander and cleaning the ISV stopped it instantly. Common issue. If cleaned and maintained it should not need replaced. Provided it is this causing the problems.