1995 Mitsubishi Galant low revs?

I have just recently bought an m reg mitsubishi galant v6 24v only to find that when I get it back to mine and try to restart the car or any thing the car is running at low rev (around 100-300) when idle if it runs at all. If I do manage to get the car running then when I go to stop at the lights or in traffic the car cuts out. I have been told its something to do with the idle stepper motor. Just want to know how I can find out the actual problem (or if you are able to tell me, but I guess that without looking at it it would be difficult) and how to possibly fix the problem. Id rather not go to the garage who round here charge alot of money just to even look at it before they can tell me the problem and then alot of garages like to try and over charge too (i also had a calibra which neede a new ignition barrel fittin which I already bout with keys and new ht lead a coil and they wanted to charge me near £300 to fix it. I managed to do it my self costing me considerably less especially for the ht lead and coil and now works a treat). Any help would be fantastic as I really dont want to have spent money on a car for nothing as this car seems to be a good car apart from the low revs. Cheers, vicky