Club 80-90 Forums

By crikey, I think you're right that he's right.. but wouldn't you notice that, fairly obvious when a throttle is sticking?

Maybe, but aren't there two movements on throttle? Or am I remembering that wrong?

Mine had rubbed where the throttle cable runs through the bodywork in front of the engine bay. There was a little sleeve that had moved but was still hiding the chafing. Took me ages to find it. The throttle seemed to be returning all the way but was occasionally just a few mm out. Quite scary in an auto.

I had precisely the same problem - 1600rpm idle, hot.

It turned out to be throttle cable & switch adjustment. No more, no less - now, rock-steady 900rpm idle.

There's a two-pin multiplug underneath the inlet manifold, by the idle valve. Put the multimeter across the switch's two pins - with the throttle closed or full open, you should see zero resistance. As you move the throttle away from full-closed or full-open, you should hear a click and it go infinite resistance. Let go of the throttle, and as it closes, you should see the switch close again.

Assuming it doesn't...
Start by slackening the throttle cable from the quadrant. That ensures that the cable being too tight isn't affecting it. Re-test.

If it's still doing it, there's a stop screw on the throttle body. I found that I needed to remove the throttle body (easy) to adjust it. Slacken it so that it behaves properly.

Without the "throttle closed" signal from the switch, the idle circuit does nothing at all.

The 'stop screw' is factory set and not supposed to be touched. It's the microswitch (only one on my throttle valve but some have two) that has an adjustment mechanism, see Haynes or Bentley.
Unplugging the ISV has the same effect as squeezing the hose doesn't it?

Hi Karl.

I had exactly the same problem not long after I got my Syncro. It turned out to be the electronic idle stabliser control unit that sits behind the offside rear light cluster and looks like a headlight relay on steroids. What had happened was that it had been left lying on the floor and had got damp inside. I opened it up very carefully, dried it out with a hairdryer and then sealed it up again with a bead of silicone. I also cable tied it up off the floor. Since then no problems on the tickover front at all. I believe that tencent in the USA thinks these things are a waste of time and disconnects them (he fits an oil cooler in that place) but I don't know what he does instead to ensure a steady idle.

I should acknowledge the help of Keeno (now sadly no longer posting on here since he got rid of his Doka) who first helped me to ID this problem after I had tried all the other stuff that has been suggested above.

Good luck with it.

Pete

Up-date........


Just spent a couple of hours (in the heaviest rain of the year!) looking at my engine.
First the throttle cable/body. Looked fine. Return spring looked/felt strong. Took cable out of clamp. Felt fine, easy movement. Discounted that.

Had a good regulator (cylinder on top of engine) & a spare relay type thing behind rear lights. So just decided to swap them in. And set up for timing set-up.

Started up & all good. 1000rpm & timing abit advanced. (Reckon AA man had advanced & turned-up tick-over screw). Bit of dizzy adjustment, quarter turn on the tick-over & engine sounding sweet as a nut at 850rpm!!

Sorry I can't tell you for definate which of the two parts it was but was not a nice day to be testing & fiddling with old VW's!!
Thanks to everyone for your help.

All you have to do now then is put them back one at a time to find the faulty part, bin it, and keep the other for (another) rainy day

It's the 'bit of a distributor timing adjustment' that worries me, never a good idea unless you know:-

a) Why (you're adjusting it)

b) Where (you're adjusting it to)

c) What the setting was before

That said, it's 5 to 2 it was the ISV or the ISCU ?

Good that you've got it sorted out though.