high idle and unstable problem

[Huw Powell]

> As I now have trouble with the idle control system of
> my car, an Audi 80(not quattro), 1988, with CIS-E M
> fuel system, I have to fix it by myself due to the
> high cost of repair by mechanics. But I don’t know too
> much my car as a new driver, it is highly appreciated
> if you could give me some instructions.

> Problem:
>  High idle speed and not stable
> Once I start the car, tach needle will gradually
> climbs to 1200rm or a little big more than that within
> a few seconds, and then runs steadily at that speed,
> instead of 1000rm(normal idle speed). Then, after one
> or two minutes, the idle problem comes. The touch
> needle (of engine speed) begins to fluctuate
> delicately but frequently around 1200rm, and the
> engine shakes accordingly.

> Discoveries and tests by myself:
> 1.Code dumped
> (1) 2231
> -Location of problem: Idle stabilization control
> limits exceeded
> -Possible reasons:  intake system leaks

That's what I'm betting.

> 2.Idle screw on throttle body.
> When I turn the idle screw (on the throttle body )
> anti-clockwise, the engine shakes, more turns, harder
> the shake will be. When I turn it clockwise, the idle
> problem will get less worse, but it is a pity that it
> cannot be turned too much, because the screw has been
> already very tight.

the screw is supposed to be closed all the way.  when you loosen it,
even more air gets in, though at least it is metered.

> 4.Only after I have started the car for a few minutes,
> the idle problem comes. In another word, during the
> first one or two minutes after I start the car, the
> engine speed is less than 1200rm, but then climbs to
> around 1200rm and begin to fluctuate.

the start up enrichment is enough to offset the excess air form the
intake leak

> 5.When the idle problem happens, if I switch on the
> A/C, the speed of engine will fall to a lower speed
> (somewhere between 1000rm to 1100rm) and can maintain
> it, no idle trouble then.

the AC loads the engine, the ECU can finally control it where it is
supposed to be.

> 7. The hose routed to intake manifold from ISV.
> Both the hose and the elbow between the hose and
> intake manifold are loose, not so tight. In other
> words, the air can leak from them. I changed the
> elbow, but it doesn’t work.

the air might be leaking in there.

> 1. What lead to the idle problem of my car?

probably excess air leaking into the intake tract...

> 2. What should I do if I fix it by myself?

carefully examine all the hoses and connections and make sure all are
good and airtight.

> 5. I ever dismantled the throttle body, but I noticed
> that the idle screw near the idle switch doesn’t
> connect to any other part of the car; it is just a
> screw only. How can the adjustment on it affect the
> idle speed and stability?

if you were supposed to use it (which you aren't, it's a relic), what it
does is allow some air to get around the throttle butterflies even when
they are closed.  if you mean the screw I think you mean.

Oh, and PS, nice to see you on here as well... good luck with your car!

--
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/