Weird idle question

[doommachine]

OK so I have been running without an ISC for ages, and as the car heats up the idle continues to rise, until it's at operating temp. I have no FIAV, it is filled with liquid metal

Anyway, I just recieved a working ISC in the mail, so that isn't an issue anymore, but I have a weird issue - when I snap the throttle off from over 1500-1800 rpm, regardless of the operating temperature or where the idle is at any given moment, the revs dip to 650 rpm for approximately one second, then return to normal. Now that I have the ISC it doesn't stall anymore, which is good, but I just want to know what's causing it - when the a/c is on it goes down to about 600 rpm, and the oil pressure drops a bit too low for my liking then...

My haltech is set so the minimum hot opening is 1% - I found if I set it to 0 it would still dip, but then open up to around 1500rpm every time I let the throttle off - annoying. I've been without a working ISC for ages, and the piston would have been all the way in at that point, and yet it was still happening.

Possibly this is a vacuum leak? Anyone had a similar issue in the past?

 

[CLuTZ]

I'd say its a tuning issue. Its hard to get cars running perfect with aftermarket ECU's!! Its even worse with cams!!

 

[doommachine]

It just seems so bizarre that it dips lower than the lowest idle point...

 

[mattrat]

mine does that.. on a cold start if i rev it up past about 2500 when its cold idle will dip to round 500 in extreme cases..

 

[doommachine]

Ah! So, have you tried unplugging your ISC to see if it still does it?

Does it do it at all when it's warmed up? The A/C seems to exacerbate it.