I haven't posted/updated in a while. Not much to report, actually, other than to say that I'm really, really discouraged. I took all the helpful comments from this thread, ordered some parts from Majestic, and took it back to the repair shop. They did a complete electrical system check including grounds, checked the two-pin coolant sensor, removed the EGR and inspected the condition of the manifold, checked the IACV and throttle body (all clean, no wear), and didn't find anything. The mechanic did discover that after 1,000 miles or so on the new plugs, that they were running rich, and carboning up. So, he replaced the NGK ZFR4F-11 plugs with NGK ZFR5F-11...the former is the OE plug for the Japanese VX and runs cooler, and the latter is the OE for the Canadian VX which runs hotter. (Mine is the Canadian version).
After driving for a few days, it's clear that none of this helped. After nearly $3,000 trying to solve this problem, I have nothing to show for my trouble. The only difference is now the idle is ~500 or so, and runs a little rough for about 30 seconds or so until the ECU adjusts and it smooths out, maybe climbing a hair higher.
I still experience bucking from a cold start, at a stop sign about 3/4ths of a mile from my house. Even when the engine warms up, driving at a constant speed in 3rd, 4th, or 5th the car will produce a subtle miss/hesitation about once per second, constantly. Now that the temperatures are quite warm, the car runs better, but I know when winter rolls around, it'll be lousy again. I wish the darn component causing the issue would actually fail, so I could replace and be done with it! I no longer have confidence in the reliability of the car, because I am certain that the coil cracking issue is not solved.
The 4F plugs were put in the last time I brought it to the shop. That Honda/Acura specialist is no longer there, so this time the car was checked over by their European/BMW specialist. He checked, and replaced the 4F plugs with the 5F when he discovered they were carboning.
I mentioned earlier in the thread this problem I have with the coils cracking and failing. I've gone through three in the past two years, and five in the past ten. I drive very few miles in this car...less than 5k a year. The shop told me that this is a "known issue," and the next time it happens to replace with an aftermarket part instead of an OE. I'm fairly certain I have a voltage problem somewhere that causes the coil to overheat and makes the plastic case fail, but everything apparently checks out, so...
The engine in this car has always had a certain "quirkiness" that I've associated with the variable timing...odd hesitation issues that are predictable during light acceleration/deceleration. But what I'm describing is a different, new problem, that is definitely a misfire. Plus, given the bucking problem when cold, which never happened when the car was running better, I'm confident that the two are connected and not normal.
I just pulled one of the 4F plugs out of the box that they gave back to me, and it looks pretty bad. I have to say, though, that, despite this hesitation problem, I'm pretty impressed with how resilient this engine is. Each time the shop would call me, triumphantly, claiming that "...we've found the problem, and replaced such-and-such," even when they replaced the injectors, I never noticed any significant change -- even when the old parts were obviously not performing to spec. The only exception to this was the igniter, which was failing. This was the only part that I diagnosed on my own, and TOLD them to replace...since they were reluctant to do so based upon the somewhat erratic stalling. (Did the igniter fail because of the same issue cracking the coil? I wonder...)
You asked about the wires. I'm assuming you mean the wiring harness, and various leads around the ignition components? They seem to be in good shape, and probably went through a lot of tugging and probing this last go-through. I replaced the spark plug cables a couple months ago with the better grade, the same point I swapped a different ECU in.
As far as the coil goes, I don't have a clue what the part number is, other than what I get when I search on Majestic: either 30120-PT3-003 or 06302-PT3-000...can't tell which. Of course, I'm suspicious when I'm told that it's a "known issue," as I've never heard this before. Seems to me like it shouldn't fail unless it's being forced to perform outside of spec, which the symptoms seem to indicate. And, each time it was obvious that they had failed, since the car wouldn't run otherwise until they were replaced.
Having lived 35 years in upstate New York, and seen various engine compartments and what salt spray will do five months each year to anything that can corrode, this car is pretty clean under the hood. I think some of the issues that northern drivers have to deal with brought on by corrosion are not issues that I have. So, electrical contacts, suspension components to a degree, etc., are in pretty good shape.
This is too much for me to read through, but I read the part about your mechanic adjusting the idle speed up to 1500 RPM. It should be 750+/-50. My VX idled great and drove great at this speed. Most likely he did this by tightening the throttle cable, which is how you do it on domestics but that is very wrong for this car. Loosen the cable so that the throttle plate can fully close, and leave only a slight amount of slack in it.
Reset the ECU.
It's not the coil. Coil and ignitors are prone to fail on these cars because they are inside the distributor. But this is something you can test using a $15 digital voltmeter from Sears or Harbor Freight. You should NEVER replace parts without confirming they are bad.
"I don't know if this is true or not, but the mechanic said that this VX model was an "experiment" by Honda, and the idea was ditched after 1995. It had so many sensors/controls, and required such precise tuning, that it didn't have the kind of long-term reliability they wanted from their cars. Our car has certainly run well these 20 years, but I wonder if we're paying for it now!"
The federal VX required precise tuning and a wideband O2 sensor like those used in race cars and many modern cars, but outside of that, it has exactly the same amount of sensors as any other Honda. It has the same long-term reliability, but it exhibits much harsher symptoms when something goes bad. On my vx, it had a tiny vacuum leak from a cracked hose, and it bucked like mad. It was a $2 fix. Honda DIDN'T abandon this "experiment". It carries on in the very successful Honda Civic HX.
You should replace the small vacuum hoses. Brake booster hose is probably okay, but check it. There's not many vacuum hoses on this car.
Bruce, I read through some more of the posts. I want to congratulate this forum's members for being so knowledgeable and helpful. That is not something you see on most auto forums (I visit a lot). I'm sorry you are feeling discouraged and I will help if I can. However, I have become intrigued by this mystery and I hope it's not inappropriate for me to ask if you are willing to sell the car. I am not shy about endlessly chasing down an issue even if it means replacing the engine. I would have to ship the car to UT, but I REALLY regret selling my little green hatch - even though I love my 05 STi. LMK firstname.lastname@example.org
@bcfromfl, It may be worth getting a basic Used Oil Analysis performed to see if you have coolant in your engine oil. I did this, because I was driving around with a head gasket leak and didn't know it.
It definitely has gotten worse in symptoms and it's to the point of increased consumption of coolant (note, my coolant level at the radiator cap would get lower and quickly...over a few days or weeks of operation from having a full system). Prior, I was simply losing fluid from the over-flow reservoir.
I'll update once the headgasket is replaced. I'm sure I'll replace the spark plugs again.