Violently cyclic idle - MC engine

[Phil Payne]

Reminder - 1990 MC engine.

OK - caught the sod doing it at rest today and hopped under the bonnet.

Not breather inflation/defaltion.  Not decel valve - pulled the connector.  Not carbon
canister - ditto.  Not throttle body switch.  Not any temperature sender - pulled and replaced
all of them.  Only the fuel frequency valve had any effect.

Somewhere I have a prototype of Orim Eman's digital duty cycle indicator - I'll try and get it
on later.

----- Original Message ----- 
From: "Marc Swanson" <mswanson at sonitrol.net>
To: "Phil Payne" <quattro at isham-research.com>
Cc: <quattro at audifans.com>
Sent: Thursday, September 09, 2004 2:21 PM
Subject: Re: Violently cyclic idle - MC engine


> Probably a useless data point, but my 88 90 quattro used to do this and
> I saw one other 90q that exhibited the same symptoms as mine.  I never
> did find the cause.
>
> When you say 'occasionally', is there any particular running condition
> that seems to make it appear more often than not?  With my car it was
> only after the engine warmed up and the cycle was more like 1k->1.5k
> every second, but it would hold at 1.5k for around a second as well,
> almost like a square wave.
>
> My 90q was mostly a backup car until I sold it a few weeks ago so it was
> 'occasional' enough not to bother me into fixing it!
>
> I'll be watching this thread to see what you/the collective come up
> with... no butchery on the wiring harness on that car though, and I had
> cleaned the ISV several times.  Also, no codes.
>
> -- 
> -Marc Swanson-
> 95.5 //S6 Avant
> 87 4ktq
> 88 90q (sold)
> www.mswanson.com/audi
>
>