vacuum leaks-would cause high, not low, idle speed

good connection on the coolant temp sensor-base idle speed is too low as it is, and should be reset to about 650rpms with the isc disco'ed

proper adjustment of the tps-should make no diff except for the idle position switch, if any

clean connections on the Idle stepper motor-this is a maybe, but not as likely as the fried isc. I'd do the resistance tests before I bought a new one just in case

Not responsible for advice not taken...