Fluctuating Idle, Help!

[Stacy Anable]

I had a similar problem to this, where the idle just couldn't make up its
mind as to where it wanted to be, after doing everything i could think of,
even replacing the ISV i unplugged the little temp sensor on top of the
water outlet on the head while it was idleing high, and the idle dropped
right down where it was supposed to be, and stayed there, i replaced it with
a new sensor ($10-20 and shucks/napa do carry these) and my idle has been
great ever since, just my experiences, i am sure other listers will have
more suggestions for you


stacy
----- Original Message -----
From: "Jim Bush" <snowman650 at chartermi.net>
To: <quattro at audifans.com>
Sent: Monday, February 18, 2002 5:13 AM
Subject: Fluctuating Idle, Help!


> Hi all,
>
> I have a '89 200TQ with 165,000 miles, I have had it for about 6 months
> and got all (well, all critical) bugs worked out. It has been running
> fine for 2 months now.
> I changed the plugs, cap and rotor and the 4 large Rad. hose clamps an
> evening last week. Drove to work the next day (about 35 miles), around
> at noon and about 5 miles back home when the trouble started. The idle
> would go down to about 500 RPM and then pop back up to about 1200 RPM
> and cycle like this until it would not be able to "catch" it and stall,
> but that was only when my foot was off the pedal. It ran fine as long as
> I was touching the pedal: acceleration, boost, drivability. It seemed to
> happen all of a sudden.
>
> I got home, cleaned the ISV (again) replaced it, no change. Then I got
> to looking around and found that the large coolant sensor under the
> upper rad. hose (near the motor) the rubber boot was filled with coolant
> so I drained that dried it out replaced it, no change. In doing this I
> found that it would idle fine until it warmed up. I then looked at the
> idle switch (front of the intake) it would idle poorly then I unplugged
> it and it ran fine for a while and then the problem started again,
> plugged it back in. I then unplugged the O2 sensor and it ran fine for a
> while and then started to idle poorly again (the same way) on the test
> drive. I also replaced the ISV with an assumed good one. They both
> seemed to be working correctly, and no difference in the idle problem.
>
> One other thing that was found is that there is a vacuum leak, not sure
> if this plays into it or not.
>
> I will pull codes tonight and post them, but does anyone have an idea??
>
>
> Sorry for the long post but Thanks in advance!
>
> Jim Bush
> Holland, MI
>
>