I have a 3 litre TS v6 which has has problems with stalling while idling when turning due to idle being too low about 500. Only does it when hot and also missed when under load. Resolved the problem intermittently by using Techron 1000 fuel system cleaner every two or three tanks but has been getting progressively worse. Based on some of the threads here decided to change out the ISC and got one from Burson's for $116 (turned out to be genuine new Mitsubishi). Following changeover idle revs immediately went up to about 1700 (revs also now go up when wheel turned). Thought this high revs may have been due to adjustments made previously (before I bought it) to get the revs up. Problem is I have now brought revs down to 800 rpm by adjusting mixture closkwise (screw on front of throttle body) but now car misses more when accelerating and appears to be using more fuel. Also screw is on the stops. Think there must be something else that needs adjusting other than this mixture screw as it appears that the ISC probably was not working. Any one got any ideas for fixing.

Did you replace the "O" ring on the ISC?
Check for air leaks in the intake from the MAF to the engine. Also check plugs and leads, see if any of the plugs are darker due to the misfire, will give you a picture of where the problem lies. Leads can be checked with a multimeter. Put some masking tape over that adjustment screw in case it is sucking air. Its not a mixture screw, it controls air flow. Possibly its time to clean out the throttle body. Have a look in the distributor cap for damage and wear. Could also be ignition coil or power transistor, or the Hall sensor in the distributor.
If it gets to that last point, pull out the distributor, power transistor and coil and have them checked by a local sparky or EFI specialist. I had to, turned out to be the faulty power transistor had taken out the coil.

No. Didn't know it had an "O" ring. Taking into account the large change in revs and that speed adjusting (SAS) screw was on clockwise stop have put old ISC back on and wound back SAS to a setting where it wont stall. Now running better at low revs as it is getting more air. Still missing though on acceleration, no air leak at SAS so will have to check the other things mentioned. What's the MAF couldn't find in the workshop manual. Thanks for your help.

MAF - mass air flow sensor, its the plug on the air cleaner box. Car runs like a dead dog it its unplugged or the contacts are dirty. Worth a look.

Thanks will have a look tomorrow afternoon