I’ve been working on this car for over a week now, replaced plugs, wires, timing belts, balance shaft belts, serpentine belts. Cleaned out egr valve, cleaned out FITV, all fluids are good, tried unplugging TPS, and still no dice.

When I first start the car, as it’s at the startup fast idle, it misses (if that’s the right word, it just slightly dips in RPM for a second) every 15 seconds, at resting ~1,100 RPM, and when I hold the pedal down and go up to ~2,500 RPM, it’s still a constant every 15 seconds. When driving the car it’s the same thing, though sometimes, not every time I’ve had the car running, it seems to be a bit more often, if I was to count to 10 it happens at second 2 and 5 maybe, my next step was maybe the O2 sensor and Fuel filter if this car has one. Do you guys have any idea what this could be? Seems like other people have similar issues but other worse factors, or more/less consistent.

 

Well, it could be the distributor, the cap, or the rotor. You said you changed plugs and wires, but still have some other things to check.

To perhaps see which cylinder is acting up, I would pull all the spark plugs, keeping them attached to the wires. Then have someone watch (preferable in the dark to make this easier to spot) while you crank and see if one of the sparks seem dimmer than the other. At least then you can narrow it down to an area to focus on.

I suppose it could be an injector that's dirty as well, that can happen. Perhaps pull those off and clean them, or run injector cleaner to see if that helps.

You could also check voltage to the injectors to see if any are lower than the other, you might have a damaged/worn wire that is causing the issue.

 

I finally had gotten through everything I could check, found a forum post of a guy saying he unplugged his O2 Sensor and that didn't help him but I tried that anyway, instantly had a smooth idle for the first time and was able to drive without the issues I was having before. I've put about 140 miles on it since then and it seems to be mostly worked out. Sometimes when I'm off throttle it seems to sputter and jerk just a small amount, though it doesn't do it every time. My next step was probably fuel filter and possibly pulling injectors and cleaning them.

Do you have any diagrams or pictures on how to check the injector wiring voltage? I'm pretty decent at physical parts but not afraid to admit electronics are not in my wheel house.

 

Well, now you've introduced an interesting piece of data. If you unplug the O2, the car can't go into normal closed loop, so it falls back on default settings, and I suspect the car runs a little rich and timing might be slighty retarded. Gas mileage might also go way down. But that mapping means it is bypassing a few things. With that, I don't think it's the injector voltage, perhaps they just need cleaning?

 

I reset the trip when I filled it up as I've read a lot of people on here documenting their mileage per tank so my plan was to do that. As I stated when I parked it yesterday I'm right at 140 miles, and If I had to guess I'm just under 3/4 of a tank. I filled it up with Premium and also put in some Lucas Injector cleaner so the advice I got from an import mechanic I know was to run this tank through and see what happens from there, I've just never worked on or driven a Honda so I have no idea what it should sound like at idle or on throttle/off throttle, I've been told if I had a more terminal issue it would be more obvious but after all the work I've done it's easy to be scared that it will just explode without warning.

I'm under the impression it sat outside for at least 2-3 months after the previous owner pushed the balance shaft seal out and didn't have time to tear it down (on top of the car having ~227,9XX miles), so It's definitely possible that almost everything about the car could still be a bit stiff or gummed up as we had record low temperatures in January of this year. The car seems to run and drive okay minus the slight hesitations and jerks that don't seem to be constant which has me leaning more towards fuel delivery. Is it worth pulling the rail and cleaning the injectors individually, or introducing some kind of solution directly to the motor like seafoam into a vacuum line? Or would you suggest anything else? I'm dreading trying to replace the fuel filter as it looks like its in a terrible spot, and the only slightly helpful video I found the guy breaks the clip holding it to the firewall trying to remove it.


Here is some more detail about the car and what I've done/replaced:
1993 Accord LX, appears to have been really well taken care of until ~4-5 years ago when it left the second owner and has changed hands through several younger owners until I bought it.

RTunes Racing "Short Ram Air Intake" (Came new in the box with the car, I installed, I know nothing about it)
Balance Shaft seal + Retainer piece.
Water Pump
Timing + Balance Shaft Belts (Timing + Tensioners set by the book to the best of my ability)
Replaced Engine mount to the right of the engine, I was told the mount to the left, and front of the engine had been replaced, I have the 4th engine mount, but Don't even know where it's at or have time to dig for it.
Valves set to specs from Manual.
New Spark Plugs + Wires (Old wires are fine, tested idle issues with both sets and detect no difference)
New Cap + Rotor (Both were in the worst condition I've ever seen, I suspected this was my issue but it only slightly helped)
New Valve Cover Gasket + Plug well Gaskets (Oil in wells when I pulled the wires the first time)
Cleaned and adjusted FITV.
Cleaned out IACV, Used RTV Make a gasket to reinstall as I suspected a vacuum leak at this point.
Cleaned Throttle body + Butterfly.
Cleaned out EGR Valve and the place on the Block the EGR installs into to the best of my ability, it was caked pretty bad with carbon.
New PCV Valve (Tested Removing and Plugging the whole in the valve cover, no difference in idle issues I had prior to unplugging O2 Sensor)
Oil Change (Used Cheap oil + filter the first time as I honestly expected to leak it all out on the floor after I had replaced the balance shaft seal, I need to drain it and put in better oil, I don't appear to be leaking or burning any oil)
New Serpentine Belts (Replaced both)
Unplugged TPS to test if that was an issue, idled terrible without this, don't suspect this to be the issue.
Topped off Coolant, it was at the MIN line, I don't suspect air in the lines.
Unplugged O2 Sensor, smooth idle, smooth when on throttle and driving, as stated before, jerks and hesitates intermittently when off throttle and coasting. No Check engine light with this plugged it, light comes on when I unplug so I suspect that would be the only CEL code I would find.
Before unplugging O2 Sensor, I had to adjust the Air bypass screw on the Throttle body open or it would idle down to ~200 RPM and die, after unplugging I had to adjust this back closed to bring idle down to consistent 800 RPM from 1,300 RPM with screw adjusted open.

 

After driving a bit more, I've determined that the issue happens ONLY under very very low throttle input, just touching the throttle 1-5% to maintain speed, or when slowly coming off the pedal to begin slowing down, in that range of just barely pushing the throttle is where the sputtering and jerking happens, all the way off throttle, and on throttle beyond that the motor runs smooth.

 

UPDATE: As a suggestion from the import mechanic I know, I pulled the vacuum line from the EGR valve and plugged it, instantly resolved the issue, and I was able to plug the O2 sensor back in without causing anymore issues, at this point we suspect the EGR valve is sticking open or has failed in someway that is introducing a vacuum leak that I couldn’t diagnose in the traditional sense, already have a new O2 sensor on the way, but I plan on removing the EGR valve and testing it does in fact leak while in the closed position and that should lead me on the right path.

 

Great job figuring it out!

Others will appreciate the data as well, as I am sure a lot of people run into this. EGR issues are common, makes sense in hindsight.

 

Update, Got a new EGR Valve, hooked it back up, Plugged in O2 Sensor and I was immediately much worse at idle and at higher RPM than before. I Unplugged EGR and O2 Sensor, Reset ECU and got back to a smooth idle with neither of those connected, reconnected O2 Sensor, Smooth idle, Reconnected EGR Valve, Smooth idle. However, now I'm back to where I was before I plugged the vacuum line going to the EGR Valve, Smooth idle, smooth increase in RPM under acceleration, but when trying to cruise (Very little throttle input), it sputters and jerks and sounds awful.

Based on a suggestion from the mechanic I loosened the EGR Valve and slipped a business card between the EGR Valve and Port (EGR Still plugged in and Vacuum connected), now I have a slightly inconsistent idle (Under fast idle on cold startup, it sputters just a bit and revs up to over 2,000 RPM, then eases down to around 1,500, then quickly goes up and down between 1,500 and 1,000 RPM, smooth but still not quite perfect idle once the car has warmed up, sometimes it drops really low and it catches itself and goes back up to around 800 RPM, other times it gets stuck at around 1,100 when coming to a stop and sitting at a light or stop sign), the sputter and jerking at very little throttle input is 100% gone in this state, and still smooth under acceleration.

I'm still waiting on a new Denso O2 Sensor to come in the mail, that also has to help as I've noticed big differences between O2 sensor being connected/disconnected.

So I'm assuming a few things here, Either the ECU is telling the EGR to operate incorrectly for some reason I haven't found yet, either It has vacuum when it shouldn't, or doesn't have vacuum when it should. I've been planning on borrowing a vacuum gauge and trying to test that line, I've been told I should have absolutely zero vacuum at idle, and If I have vacuum at idle that is a problem. What exactly would cause the ECU to direct this incorrectly? (i.e. Why would it have vacuum at idle if it shouldn't?)

It's still possible somewhat that I have a very intermittent fuel delivery issue, unplugging O2 sensor may help this as it should make the car run more rich, which basically attempts to hide whatever issue I'm actually having.

What exactly would cause this kind of issue for it to be mostly corrected by blocking off the EGR Valve/Port?

 

Because I hate coming across posts like this that have a similar issue to what I'm facing, but never get a resolution I figured I would post a final update. The inner belt tensioner pulley that sits on the pin on one side, and has a spring hooked to it on the other side, had missed the pin and was resting on the metal arm of the pulley, because of this, it wouldn't actuate on the pin as intended and could never hold the belt as tight as intended. This was 100% the cause of the random and intermittent issue, as it only seemed to happen at idle or very low rpms when the belt was getting the least assistance from moving tension.

 

The answer is intriguing. I just came across the somewhat same thing on a completely different car (e36 BMW), and it took forever to also diagnose it was the tensioners and idler pulleys coming apart slowly. Thanks for the update, that took you quite a while.