Hi: Well, I've been reading the VX threads here, and checking my car against the suggestions. Came across the PCV valve issue, where the VX version is different from the other Civic PCV valves, i.e. no spring, plunger, etc.
Then I remembered my mechanic saying something about the VX engine swap we just finished, about it having "the wrong PCV valve, with no insides". Cracked open the hood, and sure enough, he replaced the "right" PCV valve with the "wrong" one. So I took the "wrong" PCV valve, cut off the plunger/spring end, removed the "guts", and reinserted it.
Fired it up, and immediately noticed the engine "surging" from about 1000-1300 RPM. I drove it a little, and noticed a lot of black smoke from the exhaust. Went on the highway, put my foot in it and the smoke cleared up. Came back in town, drove around some, still "surging", around 800-1000 RPM. No more smoke, though.
I'm wondering if it's a dirty IACV? I visited with our mechanic again, he said he had a terrible time getting it to idle, before he replaced the PCV valve with the "wrong" one. He also mentioned the plugs in the new(er) engine were black...like the mixture was too rich...
I would order the OEM PCV valve for the VX. It has a much smaller diameter inside of it, and that should help slow down the air going through it. I don't think ripping apart a normal PCV will give you the same results.
That being said, you probably should clean the IACV since that will almost always give you a surging idle it it's clogged or bad.
Also make sure you have the correct plugs for the VX since they are specific for the motor. And don't go with platinums. Buy the NGK v-power or irridiums.
On the never-ending quest for better gas mileage...
how did it idle befor the PCV valve was installed? I'm having the same issue and I bought the correct PCV elbo from honda and still have the idle bounce.
I haven't tride pulling the "back up" fuse that clears the computer to see how that affects it, I did however have some luck with useing some carburator cleaner in the intake to clear the crud out, of course that stuff doesn't burn so it stalls the engine if used while it's running.
Also when I ordered parts from honda I ordered part number 2 and number 5 and they sent me two parts that looked like number 5, a bent elbo, one was empty and one had a spring loaded valve in it, when I installed the empty one the idle still bounced so I'm currently running with a PCV valve, in the same confused boat as you are in.
I ordered the "right" PCV valve, after arguing with the parts store guy for a while...he insisted "the PCV valve HAS to have the spring/plunger in it". I had read the VX PCV has a smaller orfice, as Danronian says to restrict the air flow. Should have it Friday or Monday, one of the joys of living out in the sticks...waiting on parts.
OK took an hour this AM to install a different IACV (from my spare VX engine) after I cleaned it thoroughly. Started it up, while in cold idle (around 1200rpm) it runs OK. After it warms up, same scenario....surging about 100-200rpm. I disconnected the sensor on the IACV and attempted to adjust the idle adjustment screw, per the Haynes manual. When I disconnected the IACV, it ran smoother (still surged though), adjustments to the screw had no effect on RPM. I went out 3 turns, back in all the way, no effect on RPM. Left it at 1 turn out, reconnected the IACV sensor, pulled the backup fuse for 30 sec., plugged back in, started car. Now it does idle slower....900 RPM or so, still surging.
Have noticed it's smoking, too...white smoke. What do you think....O2 sensor, or maybe ECU? Prior owner was a wannabe tuner, he may have screwed up the ECU.....guess I could just put in the "wrong" PCV valve, but I want it to run right!
Ok, I am going to tell you what my experience was with the IACV and idle bouncing, similar to what your describing. Take it for what it's worth, since this is not on a VX.
What I discovered, finally, was that I could plug the hose from the air filter, going into the IACV/intake manifold and when I did so, the idle settled right down. What I discovered was that the IACV had a broken tip, so it was not able to seal tightly. With the IACV unable to shut off air flow, their was to much airflow. In turn, the ecu uses the Oxygen sensor to try to maintain the idle mixture on the engine. When their is to much air, it apparently does some sort of a hunt on the time interval the injectors are turned on, trying to get a match between the fuel and air flow. However, it isn't able to do so with the extra air being allowed by the broken IACV valve, in my case, so the engine rpm modulates.
On my car, if I plug off the IACV, the car idle speed can be set to where the car will idle fine, when it's warmed up. It can be a little tricky to get it started. After I replaced the IACV valve, I readjusted the idle and it runs fine.
From what your describing, I would try blocking off the pcv valve and see if the idle will settle down. It sounds to me like excess air is getting into the intake from somewhere it shouldn't be.
I find it kind of odd that honda changed the PCV parts, the two different honda dealers that I delt with said that it has the spring loaded valve, and it does run smoother with it, and I don't think that two of us (anyone else out there?) could randomly have the same problem.
Is anyone besides 4bfox and me having this problem? and 4bfox, anything else you can tell us about your car? number of miles and so on.