I put a new L1H1 O2 sensor in my VX today. I had to use a cheater pipe to get the old one out, but I did it and didnt break anything. The technique was to cut the wires on the old one so I could get a nice long socket over the sensor. It was a gamble but it worked.
It seems to run more smoothly in lean burn now. It used to miss a little in lean burn before. It can smoothly accelerate from 1200rpm, which is a great thing. The transition between lean and regular is less severe. It also seems to have a little less power when you give it some throttle now. I also reset the ECU so that may have something to do with it.
Unfortunately when i did my compression test, my wife left the ignition on for 6 hours, running the battery down. I charged the battery, and it seems to hold a charge (it wasnt quite fully drained). Luckily nothing serious seems wrong, and hopefully there are not any damaged components.
I have noticed that sometimes when putting it in neutral, it drops to 750 (like normal) and then goes up to 1200 and back and forth 4 or 5 times. I dont like the looks of that and wonder what that could be. Anyway i wont worry yet because it only happens every once in a while. Actually it only did that a couple of times before, when it was still warming up.
Hopefully, the smooth running lean burn will help lift the MPGs...we will see.
I don't know if the D15Z1 has the same problem, but I've had two D16Z6s develop a pretty heavy, constant idle bounce resulting from a loose fast idle thermo valve. The FITV is bolted to the bottom of the throttle body and has a coolant line running to it. All Honda throttle bodies have a coolant line running to them to prevent freezing, so don't confuse any old coolant connection for an FITV.
An FITV problem is pretty easy to diagnose: Remove the air cleaner to throttle body tube and look inside the throttle body. You should see two large air ports on the rear surface of the throttle body bore. Start the engine and block the lower of the two ports. If the idle bounce stops, it's an FITV problem.
Unlike previous designs that used the EACV, the ECU relies on the FITV for cold idle boost. It's an entirely mechanical device - the required movement to open and close the valve is produced by the thermal expansion of a chunk of thermowax, just like a radiator thermostat.
The problem area is generally a plastic ring on the air side (as opposed to the coolant side) of the valve. Looking at the diagram in the OEM Civic service manual, the ring appears to do the actual sealing between the valve body and valve plunger. If you take the flat end cover off the valve (the other end's cover is domed), you should see the ring. As I recall, it's white plastic with a notch cut across it. If the plunger weren't in the way, you could stick a really big flathead screwdriver in the notch... That's pretty much what you need to do. The ring works it's way loose over time, allowing vacuum to leak past which causes a boost in idle speed when it isn't needed. All you need to do is screw the ring (it's threaded) back into the valve. The Honda service manual claims the valve is "factory adjusted", so a little tweaking of the ring position and some locktite might be in order, but I've never had problems after simply tightening it down snug against the plunger. I guess it would really depend on the temperature of the valve when you adjust it.