This is my first post so hopefully I’m doing this right lmao. I’ve got a 1996 Accord ex 5 speed that has a vibration only at idle. I’ve done basically everything I can think of to fix it with no luck.

I purchased it about a year ago, has about 280k miles and is in great shape overall.
Since I got it I’ve done a new timing belt, water pump, resealed the oil pump and pan.
valve lash adjustment, deep cleaned the intake manifold, throttle body, IACV and FITV, cleaned injectors and new fuel filter, all new motor mounts.
new plugs, wires, coil, cap and rotor, ignitor is the only thing left not new.
New accessory belts and harmonic balancer. Both 02 sensors are new, secondary is on a spacer as it came without a cat and exhaust does leak at flex pipe and needs replaced.

Idle is set correctly at 700 ish per the base idle procedure.

Idle doesn’t surge or anything, only hangs a little sometimes, coming off the gas it will sit at 1k rpm for a couple seconds then drop to 700, not all the time could just be PS.
No vacuum leaks found with a smoke machine.

No CEL.

The issue I’m having
it vibrates at idle, I don’t remember if it did when I got it but I’ve done a ton to it since then. It’s only when at idle, as soon as you give it any gas it smooths out totally, it gets worse when I turn on any accessories: defrost, hi beams, etc…
battery is a few years old but voltage while off and on look good and it doesn’t struggle to start. Battery terminals are tight and I’ve cleaned all the major ground connections.

What else could I look for here? I don’t think the timing or balance shafts are off because if so I’d think it would always vibrate and not just at idle with no throttle.

Thanks for any help.

 

Well.....I have to ask if you are sure that you have the balancer belt shafts in the right position. These 2 shafts are what the balancer belt turns. The forward one closest to the front of the engine is easy to "time."
The rear one which is driven by the oil pump sprocket is not so easy. You have to do a special procedure to keep this shaft in place especially since you indicated that you may have replaced the "racetrack" O-ring for the oil pump. I could describe the procedure, but I would be typing all day. Research this yourself on youtube maybe. The procedure boils down to removing a bolt right under the water pump and using a screwdriver or other long tool to get the shaft right. The oil pump is driven by a gear that is not 1 to1 ratio. The shaft turns 2 times for every 3 times the oil pump sprocket goes around....or something like that.



This may not be your issue, but it is the first thing that comes to my mind.........

 

Yes I did the whole thing with inserting the rod into the bolt hole to align the rear balance shaft.

 

OK, 2 other things that I have for you now.....When the car is not idling right remove the hose to the EGR valve. If this affects the idle, then follow the hoses back to the solenoid on the left front fender. I have seen the 2 hoses at the solenoid reversed after doing a timing belt job a couple of times. They get reversed because the hoses were removed to get them out of the way during T-belt installation. (FOR REAL!) There must be a one way check valve in the solenoid or something similar....... Lastly check the PCV valve on top of the valve cover. Make sure the check ball is not missing. You also cleaned the air passage around the throttle plate, but now, lube it with WD-40, so that it will move more easily -- although this is unlikely to be your issue. That"s really all I have for you. Your description sounds like a vacuum leak even though the smoke test was negative, hence maybe the EGR is hanging open. Maybe someone else here with more experience than me can contribute more???

 

I’ll check out the EGR thing, the pcv valve is brand new OEM from Honda with a new grommet. I’ll try checking for vacuum leaks again just to rule that out.

 

Welp it’s not the EGR. At idle with it vibrating I unhooked the vacuum hose from the EGR valve and that did nothing. The hose didn’t have any vacuum coming through it idk if it should or that’s just the solenoid doing its job. Even tried switching the solenoid hoses around and that had no effect either. Definitely had a strong vacuum on the supply side hose for the EGR solenoid. I popped the PCV valve off with it running as well and that did nothing. I’m starting to wonder if I have a dead cylinder or something here. It doesn’t burn oil at all from what I can tell though and still runs and pulls well other that at idle. I do notice when it’s not idling at temp, mainly on cold start or if I’m getting on it It’ll have an occasional kinda really subtle hiccup or hesitation, it’s barely even noticeable and not frequent. I doubt it’s a misfire bc I’d thing it’d set a code but idk. I don’t think it’s the fuel pressure reg bc I unplugged the vacuum hose to that and even with the hose plugged with my finger it was not happy, so that seems to be working. This is frustrating 😩

 

To check for a dead cylinder or a misfire at idle, just pull off the spark plug wires one at a time and see if the RPM's drop off. If you find that one wire/cylinder doesn't give a noticeable drop, that cylinder has a misfire at idle. Then proceed to see if it is ignition or fuel........... Since the engine seems to run OK at higher RPM's, it is probably not compression.That is what I would do based on your last post.

 

Well I have yet to figure out this vibration issue, I went ahead and replaced my injectors as I just couldn’t find anywhere locally that does cleaning and flow testing. Got my exhaust fixed so it’s not leaking anymore.

At this point I’m not totally sure what else to look at. I have new anchor motor mounts and that might be a bit part of it but I’m not really sure how I could even fix that, there seems to be no options for OEM quality mounts, might just try drilling the new ones at some point.

I also wonder if it’s maybe a IACV issue still, I’ve cleaned it twice now but I wonder if it’s sticking or something. The vibration isnt super consistent, it kinda pulses and gets worse when any power drawing accessories are on. I’ve also noticed that my idle seems to hang a bit when shifting and letting of the gas. Notably if I rev it up and then let off, the idle will stop at 1000 rpm for a second or two before dropping to 750. Sometimes it will sit a bit over 750 sometimes it seems to go a little under. I have done the base idle set procedure multiple times between fixing different things.

 

Just to be clear, you are saying that you have "vibration" at idle, not a rough idle.

I am asking because you names several things associated with resolving a rough idle.

Of all the things you mentioned, the motor mounts are responsible for cancelling vibrations. Of all the things not mentioned, the balancing shafts are also for cancelling vibrations.

Probably not the cause, but also its supposed to be 500 not 700 RPM idle.

 

It definitely seems like vibration and not rough idle but I’m not totally sure. Also yes this is really late response I know lmao.
I will add, I’ve noticed recently that it seems to be getting worse. Starting to wonder more if it’s an alternator or battery issue.
The intensity of the vibration is not consistent all the time at idle, it definitely gets worse with any accessories on, defrost, hi beams, I noticed today that even pushing down on the wiper stalk to use the quick wiper does it too, and the dash lights were dimming a little with that as well, whenever turning on an accessory the idle also drops a tiny bit, 50-100rpm.

also i noticed when im stopped, if i pump the brakes a few times it will bring the idle up which makes sense, but then letting off it will drop back to 650-700 ish and vibrate hard, seems like using vacuum stuff makes it worse too.

The vibration can get fairly bad, good enough to shake my mirror and feel it in the seat. I love this car but damn this just bugs the hell out of me all the time😩