I would look into replacing the PCV valve or rather test it to make sure it holds vacuum. Also, is there a small oil leak at the rear of the motor like a small drip or two? If so, here is the scenario I see: you step on the clutch, this moves the crank ever so slightly, but due to a weak rear main seal, and PCV valve not holding vacuum well, you now create a vacuum leak for the briefest of moments. This vacuum leak is not "monitored" air, so the idle dips, the ISV reacts to catch the dip to normalize the idle. As the PCV valve worsens and maybe along with the rear main seal also, but not necessarily, when the clutch is depressed, a bigger vacuum leak is introduced where the ISV can no longer compensate and the engine shuts off.
Next, it could be the ISV is wearing out. It's after all just an electro-mechanical part in a solenoid or electric motor of sorts so if it is getting weak in operation, it could be that it is not opening the valve enough in operation to make up for your "possible PCV" vacuum leak. Here is my caveat: Do not by any means take this info as being definitive and spend a bunch of money in swapping parts I mentioned. Do the research yourself and if it resonates with you, then act as you see fit. Good luck fellah.
Last edited by lucky_doggg7; 11-15-2012 at 10:33 PM.