Can anyone help with problem with my dual fuel TL wagon? A few weeks back the idle speed dropped right off, along with stalling while cold. As gas service was due I asked him to check ISC motor etc. He could not find anything wrong, but did reset idle to make the car more driveable.
Problem now is variable idle speed, ranging from almost stalling when cold, to over 1000rpm when at normal temperature, in neutral, and no aircond. I've had ISC motor fail before in my previous V6 TS, but that was clear cut. I'm not sure in this case, and it's a bit expensive buying one just to be wrong.
Would appreciate any ideas as to any other direction I could look.

Check the TPS (Throttle Position Sensor). Might be worth resetting the ECU etc by disconnecting the negative battery connection for 10 seconds.

Check under your passenger side footwell for coolant leaks. It is possible that coolant has got onto your ECU and fried it.

Failing that, take the car to an auto electrician to reset the TPS. Might be a good idea to bring another one from the wreckers ($20 or less) just in case it is buggered. 30 minutes work at an auto leccy shouldn't be more than $50 or so.

First thing that concerns me is the low idle at cold start up. This is not an ICS controlled thing, there is an air valve under the TB that controls fast idle at cold. Regardless of the TPS or ISC this is a mechanical item and should give you fast cold idle. If it is blocked or not functioning then there may be a large part of your problem. Usually this part gets stuck open thus causing your idle to be way too high when hot but have seen a few do the oppersite. Works similar to a thermostat where there is a wax pellet which will then expand as it warms up and close off the air valve returning to a normal idle when hot.

To check the ISC, when warm at idle switch on the aircon, revs should lift a little and then stead back roughly at normal idle, proper way is with a scan tool and see if the stepper motor is responding but if you dont have one this is the best initial step to check function.

Thanks for suggestions. With engine at normal temperature, trans in N, idle is approx 1100 rpm, put aircon on, drops to about 900, then put in D or R, drops to between 700 and 800, but is quite stable.
There can be a bit of instabilty due to an even lower idle speed in the first minute or two on a cooler morning (less than 10 deg or so), but it settles down quickly. Haven't had anything really cold yet.
It may not be relevant, but fault was intermittent for the first couple of weeks before staying on full time. Meanwhile, will have a look at fast idle setup.

When I say cold motor I mean normal moring start up, should sit between 1200 and 1400 RPM if the air bypass valve is working, sounds to me like both the ACV and the ISC are not working, perhaps get another throttle body from a wrecker and give that a go

Sorry for delay in replying - been a bit distracted with other things. As car is quite driveable, will investigate further as opportunity offers. However, thinking back, it has been quite a while since it would fast idle on startup, maybe last winter, well before current crop of problems. It does seem there may be more than one fault.
Just for good measure, the drivers window is now permanently up. Dismantled and cleaned centre console window switches, but no luck. Assuming motor is all right, as it went up ok, fault may be in hold down circuit which winds window down. Seems new switch assembly is probably needed.
Only to be expected for 175000 km, I guess, and plenty of drivers window use.

It's probaby a silly question, but regarding the engine issue, have you tried lifting the pedal with the end of your foot/shoe? I've found that since I put a different Throttle Body on (installed cruise) that the TPS was out of whack, but also the accelerator pedal seems to get stuck at around 2% or so. Essentially what this means is after driving somewhere, or using the pedal, and I drop the transmission into neutral, the revs sometimes are higher than they should be (1100 or so). If I shift to drive, the revs go to what they should (500 - 700). I'm wondering if I need to fine tune my TPS or investigate the throttle body further.

It might be worth you checking TPS aswell as what Madmagna suggested. It sounds as though you're looking at a fault somewhere on the TB which isn't unheard of.

I've had problems in the past with sticking throttle cables, but don't think it applies in this case. If my memory is correct, and that's not guaranteed, adjusting the TPS didn't affect idle speed. Mine had been shifted some time ago by a Service Dept in an effort to alter the change point for the auto box, which was not a bright idea, so I spent a bit of time resetting it to normal. I do think the Air Control Valve is probably faulty, which would account for low revs on cold start, but the varying idle revs according to load could be due to a faulty ISC motor, despite the gas serviceman telling me he thought it was ok. As suggested, another complete throttle body is looking the best option so far.

The wagon is due for a service soon, so may try and find someone who can do a fault code readout at the same time. Any suggestions for a reliable place in Perth would be appreciated.