Idle stablizer question

[Reverend]

I think i have a faulty stabilizer in my 2.1DJ syncro and i wonder does any other VAG stabilizer fit? Any ideas?

[R0B]

Mine was removed yonks ago,and the two plugs plugged together,the van runs fine without it.

[Reverend]

What is the purpose of that box anyway? Mine is plugged together as well and idle is around 3000rpm....

[R0B]

Copied from another forum.

To eliminate the Idle Stabilisation Unit, pull the 2 plugs out and plug them together and run like that for awhile it will have no noticeable effect. What it does is to stabilise the engine revs as the load on say the alternator changes. Switch on your lights, the load on the alternator increases and the ISU advances the ignition slightly to compensate. A common mistake is to time the engine with the ISU in circuit. You adjust the timing with a strobe and the ISU overrides you and you change it again until eventually the timing out enough the stop ISU working. So disconnect it and check your timing. It's been awhile since I last worked on a Type 25.

[California Dreamin]

The common mechanical Idle stabilizing unit regulates air 'by-pass' (idle speed) through sensing idle rpm..load from the alternator affecting idle (turning on lights, heated rear window etc) load affecting idle from the use of power steering or AC compressor (model dependent) and idle variation due to engine temperature (whether the vehicle is on choke) sensing load and idle and compensating where it needs to to prevent engine stalling.

If the engines idle speed is set correctly the ISU won't make any difference to idle when the engine is at running temperature and not under load. The reason for disconnecting during setup is to ensure the idle by-pass screw and throttle stop idle, aren't being compensated by additional air from the ISU. So with ISU 'disconnected' ....throttle butterfly stop set initially then the idle by-pass screw (idle speed) are set to achieve correct idle rpm at normally operating temperature without load, so when the ISU is 're-connected' it shouldn't shouldn't make any difference.

However, as said..and I stand corrected, digital ISU's alter ignition timing to control variations in idle speed.


Martin

[CovKid]

Couldn't have put that better myself - nor would I have attemped to

[bigherb]

It is a digital idling stabiliser, it works by altering the timing signal between the hall sender in the distributor and the ignition amplifier, advancing the ignition to keep the idle speed level. Fitted because the air bypass valve can be slow to react to sudden changes in idle speed.
As stated it is possible to run the engine with it bypassed.

[Reverend]

Okay, thanks for the replies. I wonder if my idle weirdness is because of some other reason then.. I have new plugs, cap, ignition unit and coil.

[danmetallic]

Okay, thanks for the replies. I wonder if my idle weirdness is because of some other reason then.. I have new plugs, cap, ignition unit and coil.

You could have a vacuum leak somewhere.


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[Reverend]

Any hotspots where it usually leaks? Im not really familiar with these petrol powered T3's, 'ive had 6 of these and 5 out of 6 were with 1.6TD engine.

[danmetallic]

Any hotspots where it usually leaks? Im not really familiar with these petrol powered T3's, 'ive had 6 of these and 5 out of 6 were with 1.6TD engine.

With the engine running spray carb cleaner around the vacuum hoses, clips etc and listen for a change in engine tone.


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[jpennington]

High idle speed on a DJ - could be a faulty idle speed control unit (ISCU). Not the little box in your pic but the black box mounted above the offside wheel arch; a power transistor in this unit often overheats and fails. When idling you should be able to feel the idle stabilization valve vibrating or hear it buzzing.

[ajsimmo]

Temp2 sender (the blue one on side of thermostat housing). If this fails, or you have a bad connection, the iscu will "see" high or infinite resistance and default to cold engine setting which opens the air bypass valve, raising the idle, moreso on a warm engine.
Try disconnecting the sender to see if it changes the idle speed. If not, bridge the pins in the plug to it - idle should drop to normal. If so, it's the sender. If not, it's most likely either the black control unit behind o/s rear light, or the wiring to it. Least likely is the air valve itself.

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[Reverend]

I've now replaced thermostat (that was stuck open) and temp 2 sensor. Now the idle is lower but it goes up-down-up-down-up-down in very fast motion.

[Reverend]

I've now a new problem. For some reason when the outside temperature is in somewhat summer-ish readings, idle is worse than ever. When we had about 10 degrees outside, idle was about normal, from 1000 to 1500 rpm. Now it is barely running when you stop at traffic lights.... any idea what to look for? I have new thermostat and temp 2 sensor.