Idle problem, '89 200 TQ MC2

[Larry C Leung]

Hello List;

My '89 200Q, MC2, chipped seems to be idling rather high, even when
totally warm. It idles about 1200+ RPM even if I blip the throttle.

I checked the Bentley, but have not had the time to do the whole
set of tests with the ammeter, and come to think of it, I'm not even
sure if my ammeter can handle 2 A.

Anyway,  I tried unplugging the ISV with a fully warm engine and the idle

dropped to an appropriate 850 RPM.

When I plugged the ISV back in, it remained at 850, even after blipping
the throttle.

As an aside, I recently replaced the engine grounds, which seemed to
help the engine running significantly, but seems to coincide with the
high idle.

Is my ISV shot, or is there likely a different problem?

TIA,

LL - NY