Club 80-90 Forums

I take it from the name it stableises the idle but what i don't under stand is how.

It goes between the Control Unit and the Coil according to the haynes manual, which i can't see how it can affect the idle from there as changing the frequency of the spark from the coil would just upset the timimg? Surely to change the idle it needs to be conected to the carb?

I read in another post that it is used when the alternator is under too much load so i'm guessing perhaps it is a large capacitor that holds a charge that maintains the voltage to the coil when the alternator output drops?

Anyone know about this?

S.

taken from a previous post by syncro simon..

The idle stabilisation unit is there to boost the revs when there is high demand from the alternator or the power steering.

sorry i still don't understand,
how does it boost the revs if it's not connected to the carb? or is it?

S.

Throttle/engine speed, on a petrol engine is controlled by the amount of air allowed into the engine by the butterfly,the idle stabilization valve by-passes the throttle butterfly to increase revs when the various sensors tell the ECU that the revs are getting low. Typical reasons for the RPM drop are engine loading from the alternator/power steering pump or air con compressor. This unit also helps to smooth out the tickover during cold start enrichment.

Martin

The idle stabalization unit monitors the engines speed. When a lower than normal idle rpm is detected, the unit will slightly alter the timing (usually advances slightly) to increase the rpm to where it should be. It is a purely electronic device which is directly connected to the ignition amplifier module. Sometimes these units can malfunction but can be bypassed without any problems simply by connecting the two plugs going into the unit together.

VWCamperfan wrote:The idle stabalization unit monitors the engines speed. When a lower than normal idle rpm is detected, the unit will slightly alter the timing (usually advances slightly) to increase the rpm to where it should be. It is a purely electronic device which is directly connected to the ignition amplifier module. Sometimes these units can malfunction but can be bypassed without any problems simply by connecting the two plugs going into the unit together.

Thats right, it fits in the wiring between the distributor and amplifier and alters the switching signal.

Am I thinking of something else?
This is the unit I was talking about:

http://www.google.co.uk/imgres?imgurl=h ... 29,r:6,s:0

martin that's the Idle Speed Control Valve.

Put the words 'Idle stabilization valve' in a google image search and it comes up with these:

http://www.google.co.uk/images?hl=en&so ... =&gs_rfai=

Tis what we called them when I was working at VW......

Martin

The pictures above are of the 'auxiliary air regulator'. It controls the amount of air bypassing the throttle valve and gives the engine a fast idle when the temp 2 sensors states that the engine is cold.

Idle stabilisation is a combined effort of timing and fuel management and air bypass, on the DJ and Dijijet 1.9s (US spec mostly) and 2e4 1.9 carb models (power steering syncro etc) there is the stabilisation unit outside the ecu and in the MV,SS etc digifant the idle stabilisation spark management is run by the ecu as that already runs the timing (no vacuum advance on the disi), both systems have an idle management controller behind the rear offside light that runs the whole idle when the idle switch on the throttle body says, ok I'm at idle please keep it at 850rpm regardless of what load is applied, how strong the wind into the inlet is, how deep in water the exhaust is, how much demand there is from the alternator, ps,ac, infact just keep it idling at 850rpm thank you, hence you can lift the clutch at idle and the engine won't generally stall as it can increase power to cope with demand;
the problems come when one of the idle bits isn't working and isn't easily understood or readily replaced then stuff gets bypassed and everything is turned up a notch or moved (timing etc.) so it will run, after a fashion and uneconomically; the complexity of the idle control system allows for good idle regardless of conditions; it's just not possible to get a base setting that will work on a stone cold engine at -10 degrees that is equally as good on a hot one at 40 degrees, but by varying the fuel, spark and air the idle stabilsation system can take a basic setting and modify it according to conditions, simples

Great info - ta

By the look of things mine is the bog standard vac advance on the dizzy type to alter the timing, with the idle stabalisation unit between the coil and amplifier.

I thought the advance/retard created by the vac/centrifugal weights on the dizzy would be enough to keep the timing right for optimal power at all rpm?. So from what u say at lower than normal idle rpm the idle stabalisation unit advances the timing slightly which gives a greater power output from each stroke and thus increases the rpm again back towards idle speed?.

So i guess if this didnt work and the idle rpm dropped it could stall? Wondering if this is what may be casuing my occasional stall when pulling upto junctions.

it could be, but the first thing to check is the switch on the throttle body is switching the idle system on, if it is then check the rest of the system