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Thread: No Power At Part Throttle, Rough Idle

  1. #1
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    No Power At Part Throttle, Rough Idle

    Hey all, new member to the board and my first time really working with Hondas. Most of my experience comes from the rotary community, and old-school stuff at that, so I don't have much experience when it comes to piston engines or factory vehicle electronics - plenty of experience with carbs and aftermarket EFI. With that brief intro out of the way here's what I'm dealing with.

    I'm looking at picking up a 1987 Accord LXi that overall is in stellar shape. Unfortunately it's been sitting a while and has developed a couple rather significant problems, the one which concerns me the most is the complete lack of power when at part throttle between approximately 2k and 3.5k rpm. The issue only shows up once up to temp and it doesn't appear right off idle. Usually I can get out into an intersection before it hits and starts acting like a really slow rev limiter. With enough throttle I can usually get past it (assuming I can get it to kick down the transmission and get the rpm up) and then it runs absolutely great to redline. I have zero experience with these cars and the issue itself seems extremely strange by itself.

    There is one code present, 12 blinks which I believe is the EGR. Took it off and checked it over; honestly not much carbon build up but the diaphragm isn't holding vacuum so I'm guessing that's the source of the error. Unfortunately cleaning it and then disabling it did nothing for the issues I'm experiencing. Saw one thread that said low coolant can cause these issues (although I have no clue how or why) so I checked that, and all is fine there too. Gauge on the dash reads where it's supposed to anyway (~45%).

    The idle issue seems mostly to be a problem with low rpm at idle, although I'm not sure exactly what rpm it is since I'm not certain what the scale is below 1k on the tach. If it sits at 1k or just below it idles nice and smoothly, but it often drops lower than that and shakes the whole car. Occasionally it will kick back up suddenly but that's not too common. Maybe a sticky IACV? Not sure. The car starts and idles great, as well as drives normally, when cold.

    The vehicle is unfortunately about 80 miles from me but I will have another chance to check it over this coming Saturday. If anyone has some ideas I would love to hear them as I quite like the vehicle and wouldn't mind taking it on, assuming I can fix the couple problems. Given it's not my vehicle presently I do not particularly want to throw parts at it, although I'm more than willing to fiddle with things. If there's any other information I can provide please let me know. Thanks!



  2. #2
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    Re: No Power At Part Throttle, Rough Idle

    Bit of an update, I ended up buying the car because aside from this issue it's just too nice to pass up. I managed to limp it the 80 miles or so and have had a bit more of a look at things and here's where we're at.

    First off, the idle screw was practically seated, so I opened it up a little to match what I was seeing as a common baseline from some research (about 1.5 turns from seated). That has the idle happier although it certainly still isn't perfect. Guessing the engine mounts are shot too regarding the rough idle but the acceleration issue is the most important currently.

    After doing a lot of perusing I finally found an 89 service manual (after many dead links) and the check procedure for code 12. I also found some folks mentioning a similar issue and that it was related to the CVC valve and air camber inside the black emission box. I had already checked the EGR valve so after popping the smog box open I had a look at things and found the air chamber to be plugged up. Blew it out with some brake-clean and a compressor and the car is definitely happier, but the issue persists. So far no engine codes have popped back up though, so I suppose that's a bit of progress.

    Next thing to check seems to be the CVC valve, although I'm not really sure how you're supposed to run the engine with the box disassembled to measure the vacuum between it and the air chamber. Perhaps I need to reread the procedure. Either way, where on earth can you find replacement CVC valves? They don't seem to show up online anywhere and there are zero 3rd gen Accords in the Pick-n-Pull's near me.

    I also have some basic tune-up parts on route to rule that out of the equation too.

    Thoughts would be greatly appreciated, and like I said, I'm brand new to working on Hondas of this era and all these weird valves are throwing me for some loops. Google even attempted to throw me off track by "correcting" CVC to PCV multiple times. Anywho, any advice welcome.

  3. #3
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    Re: No Power At Part Throttle, Rough Idle

    Some more progress today - I have a feeling it's fuel related.

    Progress began when I dumped a can of Techron in the tank and shortly thereafter the car began to run perfectly. That continued for the next 80 miles of continuous driving; no issues, no hiccups, just plain good driving. It even fixed the idle. Then I parked the car...

    Come back and the car runs like it used to, lacking power, rough idle, etc. After driving around for some time suddenly it's fixed again, and it stayed that way until I shut it off. This time I notice a new code as well, code 1, O2 Sensor A (running lean I assume).

    After repeating the "park it, start it" routine a few times it seems like it will occasionally fix it self, sometimes really quickly, sometimes not at all, and then go back to rough running on the next start up either way.

    I'm thinking that fuel is the culprit because one, the Techron made an initial difference, and two, because it always has power off idle for a couple seconds and then it falls off. The exception is at highway cruise where rpm can never drop down to idle and then it's just continuously unhappy. A filter is on order and will be here next Tuesday so I'll start with that (no clue when it was last done anyway). Hopefully that solves things, otherwise I'll move on to testing the rest of the fuel system. Part of me wonders if it could be the regulator, but we'll see. Reason being is that it's usually fine at wide open (when the regulator has no vacuum signal) and is otherwise finicky. Like I said though, we'll see.

    Cheers.

  4. #4


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    Re: No Power At Part Throttle, Rough Idle

    Quote Originally Posted by Benjamin4456 View Post
    Some more progress today - I have a feeling it's fuel related.

    Progress began when I dumped a can of Techron in the tank and shortly thereafter the car began to run perfectly. That continued for the next 80 miles of continuous driving; no issues, no hiccups, just plain good driving. It even fixed the idle. Then I parked the car...

    Come back and the car runs like it used to, lacking power, rough idle, etc. After driving around for some time suddenly it's fixed again, and it stayed that way until I shut it off. This time I notice a new code as well, code 1, O2 Sensor A (running lean I assume).

    After repeating the "park it, start it" routine a few times it seems like it will occasionally fix it self, sometimes really quickly, sometimes not at all, and then go back to rough running on the next start up either way.

    I'm thinking that fuel is the culprit because one, the Techron made an initial difference, and two, because it always has power off idle for a couple seconds and then it falls off. The exception is at highway cruise where rpm can never drop down to idle and then it's just continuously unhappy. A filter is on order and will be here next Tuesday so I'll start with that (no clue when it was last done anyway). Hopefully that solves things, otherwise I'll move on to testing the rest of the fuel system. Part of me wonders if it could be the regulator, but we'll see. Reason being is that it's usually fine at wide open (when the regulator has no vacuum signal) and is otherwise finicky. Like I said though, we'll see.

    Cheers.
    If the car sat a long time the gasoline is probably bad. There usually is a bung on the bottom of the gas tank if you wanted to drain it out and start new. New fuel filter cant hurt at all and new NGK spark plugs.

    Fuel pressure should be around 35-37 psi.

    Pulling the vacuum line off the pressure regulator and plugging it would give you about 40 psi.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    Oldblueaccord <<< MY YOUTUBE PAGE!

  5. #5
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    Re: No Power At Part Throttle, Rough Idle

    Well unfortunately it doesn't seem to be fuel related. Pressure tested alright at ~32psi with the regulator connected, and ~40psi with it disconnected. Disconnecting it also didn't change the idle issue at all like sometimes happens by itself, so at the very least I don't think it's fuel pressure related. I did replace the fuel filter, although it made no appreciable difference.

    Pretty well at a loss currently, especially because it'll just fix itself randomly but always has problems after starting. Drives alright cold, and then once at temp the problems begin. I have noticed that a lot of pressure seems to be coming out of the fuel cap, although I haven't correlated it with the problem at all. Fuel mileage is so-so with mostly in town driving yielding around 21mpg.

    Right now the only code is still O2 Sensor A. To me the issue still seems fuel delivery related, although more regarding a sensor providing false input such that the car isn't injecting as much fuel as it needs. Thought about the MAP sensor, but there's no codes for it. Reading through the service manual hasn't given me too many ideas either unfortunately, especially since my symptoms don't seem to line up great with the book.

    I have noticed I can feel sometimes when the issue fixes itself. It's not major, but when cruising it's as if I suddenly have a little more torque depending on where I'm at with the throttle. When the issue is occurring sometimes it's like a rev limiter, other times it's just a plain lack of power. I can floor it and hear the intake noise from up front, but no change in acceleration. Extremely confused here.

  6. #6
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    Re: No Power At Part Throttle, Rough Idle

    Heck, thinking back again and looking at the troubleshooting section of the manual, a bad O2 sensor can cause both a rough idle and rough running/misfires. Maybe it's just the O2 sensor? Perhaps I should try that since it's throwing the code anyway. Maybe the car fixes itself when the ECU stops taking O2 sensor input (ie. when it's been out of range long enough)? Just throwing ideas out there.

  7. #7
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    Re: No Power At Part Throttle, Rough Idle

    Well um, it's fixed now. It was the frickin O2 sensor after all (I replaced it)... Multiple starts, 75 miles of driving, and we're still problem free so for now I'm gonna say it's fixed. Thanks for the moral support I suppose, or at the very least for somewhere for me to jot down my thoughts.

    If you don't hear an update on this thread assume all is well. This car certainly has some other quirks to sort out now that it's running right, but I'll address those in the future.

    Cheers.

  8. #8


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    Re: No Power At Part Throttle, Rough Idle

    Quote Originally Posted by Benjamin4456 View Post
    Well um, it's fixed now. It was the frickin O2 sensor after all (I replaced it)... Multiple starts, 75 miles of driving, and we're still problem free so for now I'm gonna say it's fixed. Thanks for the moral support I suppose, or at the very least for somewhere for me to jot down my thoughts.

    If you don't hear an update on this thread assume all is well. This car certainly has some other quirks to sort out now that it's running right, but I'll address those in the future.

    Cheers.

    Great job.

    This cars fuel injection is pretty well sorted out for the year made and all. Its a little slow throttle response wise is all.
    1988 Lxi owner since August 1995
    336k miles running strong!
    Now running E85.

    Oldblueaccord <<< MY YOUTUBE PAGE!

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