it just started today that when the car is idling (fully warm engine), if i blip/rev the throttle in neutral, the idle drops very low to the point where the engine shakes (about to die). idle vacuum reads between 400-450mm (15.75-17.72inch). i took it out for a drive and it still pulls strongly and smoothly. when i disengage the clutch, the revs dont drop much beyond normal idle. it only drops low when its idling and i rev or blip the throttle. i did a search and only came up with the possibility of the ISC. any other ideas? plugs? wires?

 

Could also be a grounding issue. Mine does a smiliar thing. You can watch on the PFC - your volts will spike/drop when it does that.

 

The ISC is an easy check. Put an electrical load on the car: Headlights and rear defogger, then unplug the ISC to see if the idle changes. You mught even be able to hear it operating.

Your dashpot might be worth checking as well.