I have a 1993 Verada 3.0 and sometimes the engine idles at high rpm anywhere
between the normal 800 all the way to 2000rpm like at 1200, 1400, 1700 and 1950.
Sometimes it revs up and down as if I'm pumping the accelerator. Sometimes at one
set of trafic lights, it'll idle high, at next lights its low, then a few sets of lights later,
its back to high. Sometimes it'll idle ok for a few days, other times it'll idle high for
a few days. Theres no set pattern.

Its really embarassing at the lights - sometimes I turn it off.

Its been fitted with lpg but the problem existed before the conversion.

Any ideas?

Thanks

Idle stepper motor, also called idle speed control, or just ISC. Do a search. Lots of info, been covered before many times.

Thanks Madmax, did a search, saw a few articles. Can you tell me where it is & what does it look like. I do have some knowledge of cars but never heard of an isc.

Its on the throttle body, has a six pin plug attached to it. Plug might be loose or more likely the stepper motor has burnt out. It controls the engine idle speed under different conditions of engine load, hence the name. Visit the local wrecker. All magnas have the same ISC so it doesn't matter what car it comes from. Ask them for a warranty, they will mark it so that if it doesn't improve things you can return it. And download the manual from this forum (again, search).

Usually a stuffed ISC will give you a low idle, not one that is all over the place, so it might just be a loose/dirty connection or an air leak.
While you are under the bonnet check that the air pipe connections are tight and that there are no air leaks anywhere. Run a 12 mm spanner over the bolts on the throttle body (not too tight, they only thread into aluminium). Also check electrical connections around that side of the engine, especially the MAF (Mass Air flow sensor) connection on the big black box the air cleaner sits in. Perhaps pull off the plugs and check for corrosion? They are all clipped on so don't just try to pull them off. lol

If everything is running ok the engine should initially spin at about 1800 rpm on startup, then settle quickly to about 800 rpm. Should stay there when you load up the engine - put an auto in gear, or turn the lights or aircon on, or turn the wheel while stationary.

I found it, might take it to the mechanic on monday.

Actually, the engine does have a low idle problem too but it seems to have started after the lpg conversion. But I have to take it back for the initial 1000km checkover which is about now. Hmmm, might see the lpg bloke first.

Well, I got it fixed - a new ISC @ $117 with free labour . Dont know if thats a good price but what could I do?