I did a B18B swap a couple months ago. Everything 100% stock from the ECU to the headers. I re did its entire intake side. Cleaned out IM, new gaskets, o-rings, vacuum lines, etc. Upon starting it up, the fast idle behaved normally as it should, but the idle never dropped below 1100 even with the adjustment screw on the TB down all the way. It's a steady idle, not fluctuating so iv been driving it just fine. I took a look at it recently and noticed a few of the I'M mounting nuts were loose so I figured the vacuum leak was coming from there. I fixed that issue, and the idle went down a little bit. I know it's running rich from looking at plugs and a slight smell, and I think it's because of another vacuum leak. The ECU trying to correct for the additional intake air and running a lil too much fuel. Anyway, my question is are there any long term effects of running slightly rich? Any possible damage to the internals or sensors? Anything of that nature.

 

a little rich, no, nothing bad will happen. a decent amount rich and it will start thinning the oil out and washing oil off the cyl walls.

get a smoke test done to find any remaining vacuum leaks.