Curious Idle bump MPH dependent (New IAC)

[EvanH]

Hi all. I put this in the facebook group, but wanted to have it here too.

I replaced my IAC. So now I have good idle, good hot starts without holding the pedal slightly, idle kicks up for AC and PS to include when the fans come on.

BUT, something that has never happened in 18 years of owning the car. If I coast up through about 15mph, in neutral, my idle jumps up from 700 ish to 1400 ish. If I coast down through 15mph ish, my idle will drop back down. I can be at highway speed (60) push the clutch, let off gas pedal, engine rpm drops to 1400 and holds. All until I slow till 15ish. Engine cold or hot. So if I slow with my gears, and the mph is higher than 15, and rpm is around 1400 the car will wanna pull itself.

Engine vacuum above 18(book says approx 19)166k miles
Idle with the brown plug and pin 10 of the diag port grounded ~700
Before new IAC, base timing was about 6
I replaced my old IAC and swapped a TPS that was known good. (Vacuum and idle did not change)
Cold idle 1400 and falls consistently until shortly before low fan kicks on.

VAC gauge.jpg