Hi, I just registered here and since I do believe I have an issue of my own I did not search for a solution.
Here it goes, I got a 87 civic that was put in a D15b2 so a few things were changed. This, was made by the previous owner and a few years ago.
I had the worst mechanic in the world, he got my idle control valve blocked so it was not working.
New mechanic replaced ECU and now the car runs way better, apart from when I start it it idles around 1400 rpm, then, sometimes once it warms up idle goes down to 750-800 rpm. Other times, most of them it only lowers to 1000 rpm, and no matter for how long I drive it, rpms remain at it. BUT, if I make a quick stop and turn engine off and back on in a short period of time it lowers to the desired 750-800.
I checked for vacuum leaks, coolant is fine, cleaned the TB and aic valve.
Since this is intermittent, what could it be? Thanks in advance!
Ps: my mechanic skills pretty much go as far as opening the hood and looking at the abyss for days.

 

Sounds like it could be your idle adjustment (usually by your carburetor/fuel injector).