The idle stop screw shouldn't be fiddled with, it is set in the factory and will never need to be adjusted. I would recommend taking the car to a Magna mechanic (eg. Mal) who will be able to reset it using a MUTII.

Anyhoo, there is a separate circuit in the TPS that acts as a switch, aside from the pot function for throttle position. If the TPS is out of adjustment or the throttle isn't always closing properly this switch won't trip and the ECU won't switch to idle mode, where the ISC regulates idle speed. The full TPS checking procedure is here, with separate sections for whether you have traction control or not: