Have you checked the zero position with the key on? It's like a 1 minute job to remove the air filter and see where the plate is. AFAIK
if the plate is too high - which is VERY common it seems - the resistance from the pot is still the same _above_ the correct zero position as to when it is in the correct zero position. The same resistance should be shown all the way down to the basic position - the bottom of the vertical cylinder..
Now, if the plate is high and above the top of the vertical cylinder - the correct zero position - IMO there will be additional, unmetered airflow entering the engine. This (again IMO) will result in a high erratic idle. The AFM being calibrated to expect a certain leak when the throttle plate is in the zero-basic position only.
FWIW you can test the throttle position switch at the harness pickup located on the intake manifold runners near cyl 1 - you can't actually check it at the throttle body itself, it's sealed - ie no plug.