Clamping or plugging the intake hose to the IAC seems the only way to stop an intermitant high idle on my '87 B230F. The high idle comes and goes (usually only once or twice per drive), but it happens every time I drive, sometimes lasting for 10-15 seconds (usually just after start) while others times for many minutes (after the engine is warm). Rpms can, and often do, exceed 3500. I've cleaned TB, replaced IAC, reset base idle speed per Haynes, the TPS "clicks". With the IAC blocked off, the cars idles fine. I have been sputtering a little and spitting black smoke since I did it, but I assume this is unrelated as it did this before on occasion, but who knows? Is there any long term repercussions from blocking off the IAC? Also, my only other thought is that electrical part of the IAC is malfunctioning. The wires look OK all the way into the FPR, but maybe the ECU? Lastly, is it possible for an oxygen sensor to cause idle problems of this magnitude? I have no idea when, and if, it was ever changed by PO (car has 170,000 miles on it). Any thoughts?

Jeff