Now that the car runs and drives daily fairly well and I'm hunting down the bugs one by one, I'd like to revisit this idle issue again. I've established from both observation and just asking online and in person, that quite a few B230's idle rough to one degree or another. There is the odd smooth one, but I haven't seen one yet.

Anyway, I pulled the motor on this 86 awhile back (1K ago), and it ran this way pretty much before. I replaced the AMM with a reman when I observed an intake backfire when tapping the throttle with the engine cold, and just slightly off running in general. That fixed that. The 02 is new. Plugs wires cap rotor new.
Hall sensor new. Intake hose new. Flame trap cleaned, hoses good, etc. Intake gasket and seals new, all other gaskets excepting head gasket new. Wiring harness is non-rotting factory replacement. The in-tank pump is new, the hoses are good, the external pump is smooth and quiet looking to have been replaced not long ago, fuel filter and tank sock new. Timing belt and all that done, balancer is new (and marked for the day it finally slips), I've run the ignition timing all around the stock spec. The vacuum lines are all new. The vacuum unit on the spark box holds fine. The throttle body is adjusted correctly. The TPS switch works and is adjusted. The idle control motor is cleaned and seems to work (it idles at about the right speed anyway). The valves were adjusted when I had the motor on the stand and the cam was out for valve stem seals. The injectors have new seals, and were cleaned by hand carefully as I've always done. I also cleaned the oil pan inside and ipoxy'd those pickup tube o-rings, but that's not really related. Anyway, it's pretty tight and dry underhood now.

So, vacuum leak? With a cold motor I emptied a can of either on top, under the intake, all over, and no change, nada. I think I've addressed all the vacuum leaks.

It has piston slap. Not a really bad case, but it's there. Get it really good and hot and it's faint, normal cruising around you can hear it, and it's very there cold, typical. I've often wondered if piston slap was screwing with the knock sensor/timing, but I've never been able to verify it with a timing light. But it's a thought.

I have not run a compression check yet. The car has north of 240K, but I don't think too far north. I do have pretty decent service records for it since 150K or so. It uses no oil to speak of so far. It starts fine, runs to redline smoothly, has what I suspect is normal power for a NA B230F with some age on it, and does not smoke. So I can't imagine it has a cylinder that down. Valve not sealing? Maybe, haven't done a leakdown yet either, but it sure runs good above idle. This is my next step I suppose.

The only other observation I have, and I've been nudged this way by a few people that have observed this in LH-Jet B230's themselves before/after swapping to stand alone engine management systems, is the ECU is doing something less than graceful to the air/fuel ratio at idle. A hint at this that made me suspect was the first few seconds of cold running it seems to run smoother, though with elevated RPM so that may be masking it. And it's worse hot. If you drive around, park for 10 minutes and let it heat soak, the misses at idle will become pronounced. They are irregular and never actually a stumble or enough to make the ICV intervene, but you can feel them. It's enough that I try and not sit at idle after such, I get underway as soon as I can for a spell. It's possible with the weather warming up things will become more interesting.

Thoughts? Anything I've missed?