Violently cyclic idle - MC engine

[sherrow at westol.com]

I missed some of the earlier discussions. In the past I have seen this
caused by a failed ISV. Engine vacuum overcomes the ISV solenoids return
spring strength which causes the idle to increase. The 1500 rpm or so I
believe is a cut off point at which the engine can not idle above (This
means your TPS is working). Either the decel valve of the fuel gets cut I
don't remember which.

Original Message:
-----------------
From: Marc Swanson mswanson at sonitrol.net
Date: Thu, 09 Sep 2004 08:21:26 -0400
To: quattro at isham-research.com, quattro at audifans.com
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


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