Fuel cut while cruising at low speeds

[A18A]

You know how the ECU cuts fuel to the engine when decelerating? well I'm pretty sure my car is doing that to me on & off while I'm driving along, similar to the speed governor at 190kph, but at low speeds (around 40-60kph usually) anywhere where there is pretty much no load on the motor (completely stock H22A, M2A4, P13 ECU). I'm BARELY touching the throttle to maintain this speed.

I guess that the ECU thinks I'm decelerating half the time since I'm literally, just touching it enough so the pedal moves. I have set my TPS correctly I think (.5v closed & 4.5 WOT?). I assume the ECU gets its signal from this to decide when to cut fuel. Does that sound right? How can I prevent my car from doing this in the aforementioned circumstances?

And just to nit-pick even more, the revs lag (only going down, not up), ie when driving slowly like a nana, you press the clutch in so you can change gear, the car will take about 1 second for the revs to drop (they should drop as soon as I let off the pedal). there are no vacuum leaks either

I think the throttle cable could be a contributing factor since it's not as 'free-moving' as I'd like it to be. I was thinking a stronger spring on the TB for the throttle plate so it would spring back to closed position more... tightly? (can't think of the word)

With the TPS disconnected, the car drives very smoothly and doesn't do any of the above issues. What are your thoughts?

[ON_N20]

With the TPS disconnected, the car drives very smoothly and doesn't do any of the above issues. What are your thoughts?

If the problem is goes away with the TPS disconnected, then the problem may be related to that. The computer will calculate values based off the other sensors such as MAP, since the TPS is gone. Could be a mis-adjusted TPS, or the TPS may have a dead spot in it that you only hit at light cruising speed. That can happen occasionally since the TPS will wear most at cruising speed because the internal wiper on the potentiometer brushes more at that one spot, and can wear through and create a dead spot.

Does the car jerk and come back on its own, or does it just cut out and not return normally until you adjust the throttle again?

[A18A]

Good point actually. I never thought about it like that, I'll replace the TPS. The car does jerk and come back on its own wihout me adjusting the throttle.

This isn't the first honda that I've had with this problem either.

[A18A]

I had a feeling the TPS broke after I had mad wheel hop & got a CEL. that's what happens when I don't have a front torque mount. never mind, I have a TPS on there now that actually fits properly. now I just need my multimeter back so I can adjust it and set it right. hopefully it goes good after that

[A18A]

well 2 more TPSs later after thoroughly checking it out, installing it, adjusting it to specs (.49v closed & 4.51v WOT, best I could get it) that fixed the fuel-cut issue, YAY. Car is very smooth to drive on flat roads at any speed that I was having problems with before. now just to fix the problem with it lagging to drop revs. I'm guessing something idle related since it has that typical honda washing-machine like idle?

[GhostAccord]

Washing-machine like idle????? Do you mean a surging idle where the RPMs go up and down? Does it only do it after it's warm, when it's cold or both?

Could try cleaning your throttle body, IACV and FITV.

If it only does it after the engine has warmed up. Your FITV could be out of adjustment. or an issue with the ECT sensor/air bubbles in the coolant

[Jack93prj]

When you mean that when you let off the gas the revs hang just for a second and than start dropping? I mean i call it rev hang and Its due to a heavy flywheel and when you put in the clutch the flywheel has rotating mass that doesn't lose speed very quickly. I put in a 8lb flywheel and love it.

[ON_N20]

well 2 more TPSs later after thoroughly checking it out, installing it, adjusting it to specs (.49v closed & 4.51v WOT, best I could get it) that fixed the fuel-cut issue, YAY. Car is very smooth to drive on flat roads at any speed that I was having problems with before. now just to fix the problem with it lagging to drop revs. I'm guessing something idle related since it has that typical honda washing-machine like idle?

Glad to hear that fixed it!
If your having a problem with the idle fix that first. I agree with GhostAccord in checking those things, also check for a vacuum leak, that will cause a very erratic idle.
Personally I've always thought my car hangs a bit on the revs in between a shift, but thats due mainly to the weight of the flywheel and engine design. My other accord will rev down a little faster but thats with a lightened flywheel. In your case if you have an idle issue or vacuum leak, that could contribute to the lag in RPM drop speed also.

[A18A]

Well I pulled both the IACV & FITV off (note, no water came out of their water lines), they looked all good, but i gave them a good cleaning anyway, put it all back together, installed them. That didn't fix the bouncy idle issue, but now with the car running, I block the TB off with my hand to stall the engine, and I lose all vacuum from around the FITV area about 3-4 seconds after the motor dies. wtf? It has always held vacuum when I blocked off the TB to check for leaks. so off it came again, this time I whored it in lots of sealent where all the O-rings are, still does the same. fuck.

I tried to bleed the cooling system, loosened the bleed valve, nada, zip, zero. nothing came out at all. I feel the top radiator hose, it's hot, I feel the lower hose, it's still cold as if the car hasn't even been running. Now I don't know how this all works properly, but I suspected a stuck thermostat. I pulled just the thermostat out and put the housing back on, just decided to run without a thermostat for now. Well now the car doesn't get warm (as expected lol), but it doesn't do it's bouncy idle anymore. I guess that may be because coolant probably flows through the IACV & FITV now?

I also stuck a different spring on the TB for the accelerator, so now it's a lot more springy-back, no more putting my foot under the pedal to pull it out when in doubt

Soooo I hope with a good thermostat, it should run all good again. I still would like to know where the vacuum leak around the FITV is though

[A18A]

Well thermostat tested mint, I put that back in. I decided to change the upper radiator hose cause it looked ugly, found out where it connects to the radiator was mostly blocked off by a bit of tape (my fault) so I fixed that. Found the vacuum leak in the FITV area, it was a heater valve hose came off its diaphram. I replaced the IACV again, start the car up and no more bouncy idle (YAY) I block the TB with my hand again, this time it held vacuum just like it should, I held it for a good 20 seconds with no sign of it losing vacuum (now I have a big red mark on my hand lol)

So it's running good, and when left idling, it will idle at around 750-800 RPM, and feels like a good running H22A w0oOT.

Now to be REALLY picky, the revs still hang a bit, but I guess that must be cause of the flywheel as previously mentioned. Other than that, and it's odd misfire every now & then (dizzy), it's fine

[A18A]

okay so it's doing its fuel cut thing again. TPS is still within spec. it is a used one, but with the way honda prices their stuff, I could probably buy another car for the cost of a new TPS from them.

Anyway, now, if I start the car when it's cold, i can drive it for hours without any fuel cut problems as long as I don't turn the engine off. once I do that, and start it any time before it cools back down, I will have the fuel-cut issue when cruising. also at the same time it's lacking power as if I've got a car full of people

I have other TPS's I could use which show .5v CT & 4.5v WOT, but the resistance of them is slightly out of allowed tolerances. I just find it a hassle to replace it since the TB has to come off, and then I have to drive the car for ages wasting my petrol to find out if it works.

Could it be any other sensors? What do now?

another thing, very randomly it just dies (not sure if it's a loss of fuel or ignition) for a couple seconds while driving in the lower rpm. guess it could be the fuel filter since it's just a spare one I had floating around when I done the swap. don't think it's related to the fuel-cut-while-cruising issue though

oh I also noticed that the speed cut doesn't work, though the ECU does get a VSS signal, and no CEL. dunno why that is

[deevergote]

Your issues remind me of the problems uslspct is having with his car. Everything that SHOULD fix the problems isn't doing the job.

The fuel cut issue could possibly be related to the oxygen sensor. I've had an issue with mine in the past. It didn't throw a code, but it would cause the engine to bog dangerously as I was accelerating (like, into traffic!) The only way to get out of the bog was to go WOT.

I would try replacing the o2 sensor with a Denso or NTK/NGK unit, if it hasn't already been replaced recently.
You might also want to look into a new ECU.


As for your erratic idle issue, you said no coolant came from the lines when you removed them when adjusting the FITV and IACV? That could be an indication of air in your system. I believe air bubbles in your coolant system can cause idle issues. Try properly bleeding the system.




And holy crap.... I just looked through your thread on 3geez... now I understand how no torque mount resulted in a broken TPS!

[A18A]

haha yup not much free room in my engine bay.

I fixed the coolant issues a while ago, I can't remember what they where exactly but I do remember a bit of tape blocking the upper radiator hose where I had to horily attach it to my radiator. it idles properly now too.

good call on the o2 sensor, I do vaguely remember the wires going into it getting squashed some time ago. I'll replace that tomorrow with a known good one (they're expensive too, so my used ones will have to do )

[deevergote]

I don't know if RockAuto.com will ship to New Zealand, but if they do, they sell Denso sensors for under $40 USD... that's quite cheap. I don't imagine a little sensor would be THAT expensive to ship!

[A18A]

WOF & rego is due = can't buy stuff because poor. I should have thought about that before doing the swap lol.

but I did swap the O2 for another one that came off a mint running car, it made no difference to how the car behaved though

oh and to add to the list of problems, another thing which only happened maybe 3 times (couple months ago) since I've done the swap, but when flooring it, say through 2nd gear, the revs would just stick at around 5000-6000 RPM for about 2 seconds before shooting off again. didn't bounce or anything, just sat there (wasn't vtec oil pressure switch). very random, those 3 times it done that was all within a week.

so going by these random symptoms, you could be right with it being a faulty ECU. I do sorta remember the car it came from had some shoddy wiring around it. possibly related.

will probably swap that tomorrow. don't have any P13s, so no vtax for me if it is a ECU fault.