Engine revs after I engage the clutch - look -

5thgen4dr5thgen4dr Band Wagon
in Engine & Drivetrain
1989 Civic wagon with 1990 d16a6 with stock manifold

When I let off the gas the motor stays at that rpm for a moment then slowly returns back to normal idle. not so bad when I'm sitting still but when I'm driving, say starting off I let out on the clutch and get going and speed up thru the gear and I hit the clutch and let off the gas to shift and the rpm's kind of linger for a moment then start to decline so by the time I'm ready to put it in the next gear the rpm's are still to high and I let out on the clutch and it slips a little bit.

The throttle is lingering when I let off.
It idles at the right rpm - 800 or so
The throttle cable is taught.
No intake manifold leaks that I know of(checked with brakleen)

There is a big exhaust leakabout half way back.

Need to get this fixed, it's annoying not being able to shift as fast as I'd like and not sure if it's affectig my mileage.

Comments

  • HaydzHaydz Moderator
    It sounds like either your TB is sticking or your clutch is slipping. It's not clear which by your description.

    Have you adjusted your throttle cable recently? Often this is the cause of a sticking TB. I'd also suggest cleaning the gunk out with TB cleaner.
  • skinnyskinny Senior Wagonist
    When I got mine. the TB was sticking bad. I took the intake off and got a rag and cleaned it out. for some reason the motor was sucking oil into the intake from the valve cover. come to think of it every honda i have had did this. Your TPS could be off too.




    Scratch that. There is a vacume thingy hooked to the throttle actuator i guess its called. Happened on my integra. two screws and it was removed. let me try and find a pic for you so you can remove it.
  • skinnyskinny Senior Wagonist
    here you go
  • 5thgen4dr5thgen4dr Band Wagon
    I believe that's called a throttle decel valve, you're saying I should take it off?

    I'll try the tb cleaner and when I did a swap on this car I broke off the end of the tps sensor then ziptied it all back together, just the part that clips to the harness was broken, the pins on the sensor were still in there..

    What should I use to clean the tB?
  • skinnyskinny Senior Wagonist
    Get a new TPS first. we had the problem with the integra it would sustain a given rpm with the clutch disengaged for a few seconds then drop back down. the pedal itself would travel freely but the TB would be kept open by that valve. You will also need to plug the vacume line attached to the unit. As far as I know a TPS is a TPS so you may be able to grab the one off your old motor if you still have it. If not pm me and I will grab one at the yard and send it to you.



    Edit: I didnt use anything to clean it out. Just a cloth and elbow greese. Carb cleaner will work as well.
  • bam-bambam-bam Council Member
    That valve thingy is called a throttle dashpot...don't ask me why it's called that, but its purpose is to keep the throttle from closing too rapidly: You let off the gas and intake vacuum rises, pulling up the dashpot diaphragm. It's essentially a shock absorber for your throttle valve. The butterfly return spring overcomes the vacuum diaphragm's resistance and closes, just more gently. Dashpots are more common on auto trans. cars, because when you let off the throttle the rpms drop below the torque converter's stall threshold and you get a stumble.
    Driveability complaint is usually opposite what you have: rpms drop TOO fast. In other words, the dashpot is ugly and unnecessary, but probably not your problem.


    Lube the throttle cable, check the Throttle body spring. Don't worry about TPS unless you have a code. Keep it simple.
  • 5thgen4dr5thgen4dr Band Wagon
    Yeah I'm thinking not TPS becasue I have no code but I have thos up the ying yang so I'll replace that, I'll grab some carb cleaner today and clean/wipe out the TB real good.
    I'll get back you ya's today.

    ANybody looking for soe cheap coilovers? this wagon came dumped and I'd like to put the stock suspension back on.
  • skinnyskinny Senior Wagonist
    I would buy them but I already went skunk2. I know when my tps was off just a lil it was making the car run like shit. your may be fine but it could also be off instead of TDC
  • lucskywalkerlucskywalker Wagonist
    you had said throttle cable is tight, wich sounds like the first place to start. should not be tight at all. i little play is the way its supposed to be. when things heat up they expand, and yes so do cables. tps is never set to tdc, they are adjusted, to a specific ohm's. funny these r replacable on jdm models, but the usa got idiot screws, im shure many people have some creative ways to take them out lol, but mainly the tps bolts usdm are like this because of the settings. and we are lazy
    :D
  • skinnyskinny Senior Wagonist
    I take a hack saw and cut a grove in it so I can use a flat head then replace with alen bolts or what ever. When I did my swap in my 93 si I hit the TPS and it knocked it to 12% and I was having a lot of problems. Hooked up the data logger with the car on but not running and saw it was at 12% so I did the hack saw trick and set it to 0. You can also set it retarded and thats not good. makes you have to push the pedal down alot before it registers positive and makes the car hope and jump and run like poo.
  • bam-bambam-bam Council Member
    On the topic of TPS screws: bicycle water bottle cage bolts are perfect replacements. The ones I use are even stainless steel. You don't have to cut a groove in the old ones, either. You can just tap it loose with the corner of a flat-blade screwdriver- they're not that tight.
  • skinnyskinny Senior Wagonist
    So 5thgen needs to get back on and tell us if he fixxed it and what the problem was. Im very interested in who made the right guess.
  • udubrx7udubrx7 Senior Wagonist
    Sorry for digging up an older thread, but this showed up in a google search about the throttle body dashpot.

    From my experience, the problem of the engine not dropping revs as soon as you let off the gas is caused by a function of the EACV when the idle adjustment screw is the throttle body isn't properly adjusted. I had this problem, and I could get it to go away one of two ways:

    One: disconnect the EACV and just drive around like that. (not recommended)

    Two: Adjusting the idle screw with the EACV plugged in.

    According to the service manual, all cars 88 or later, you must disconnect the EACV before adjusting the idle screw. Then you have to turn off the car and reset the ecu. THEN you can plug the EACV back in and start the car. This is to prevent the ECU from attempting to adjust the idle itself with the EACV while you are adjusting it with the idle screw. If you are having trouble with the revs not dropping right when you let off the gas, try adjusting the idle slightly with the EACV plugged in.

    When you start messing with the idle systems like this it can get complicated, as I'm sure many of you know.
    If you can't get the car to act normal when you let off the gas, and you can't get the idle to set properly, or both of these problems at the same time - then you have another problem somewhere! Check the EACV and all your vacuum lines. Sometimes the diaphragm in the dashpot on top of the throttle can tear and cause a constant vacuum leak. Check your throttle body and intake manifold mounting nuts and make sure you used the proper gasket if you took them apart once.

    hope that helps somebody,

    Tom
  • red96turbolsred96turbols Band Wagon
    Sorry for digging up an old thread, but searching on google brought this to my attention, and it doesn't seem that it will fix my problem...

    I have a 87 teg with a D16A1 in it, there is no dashpot on this model, or previous owner removed it.

    NOW, whenever I have the vacuum line next to the red evap hose on the TB, the throttle "sticks" just passed idle when letting off, in order for it to release i have to tap the gas pedal and let it close abruptly.

    If I remove the vacuum line, the engine wants to die, but the throttle is moved much, much easier and its not held shut so to speak...

    Now there are 3 vacuum lines on the IM/TB total that are being used, and returned into a black vacuum distribution block? If i unplug all 3 of them (2 in back of IM and 1 on TB) the car idles, but rough.

    My question is, is there a way to remove that black control box and route the vacuum lines to where my throttle opens smooth and closes like it should? Car did have Cruise but it was removed by previous owner. ..

    EDIT: I don't believe it has to do with the EAVC as i can manually get it to stick in one spot, and then forcibly push it back to idle, it only happens in the first slight turn of the throttle, and like i said, with the vacuum lines off it doesn't stick, closed or open.
  • udubrx7udubrx7 Senior Wagonist
    I'm not exactly familiar with that car or engine, and I'm not sure what you mean by "black control box" or "vacuum distribution block." Could you take a picture of it? Are you talking about the EVAP purge control solenoid and map sensor that are on a bracket on the firewall behind the TB?

    It sounds like you might need to fix/replace the throttle control dashpot/diaphragm. I would definitely try to fix the system before worrying about how to remove it. I would start by lubing up all of the mechanical pieces and make sure it is not sticking somewhere. If that doesn't seem to help you can try and take the little screws out of the dashpot, and remove it's cover to check the diaphragm. Be careful when you do this because it is spring loaded (not a lot of force), so don't let it just pop apart, you might lose something. After you get that cover off you should be able to tell if the rubber flap that is the diaphragm is damaged.

    And it doesn't hurt to ask, are you getting any error codes from the ECU?
  • mikefinlymikefinly Band Wagon
    bam-bam wrote:
    That valve thingy is called a throttle dashpot...don't ask me why it's called that, but its purpose is to keep the throttle from closing too rapidly: You let off the gas and intake vacuum rises, pulling up the dashpot diaphragm. It's essentially a shock absorber for your throttle valve. The butterfly return spring overcomes the vacuum diaphragm's resistance and closes, just more gently. Dashpots are more common on auto trans. cars, because when you let off the throttle the rpms drop below the torque converter's stall threshold and you get a stumble.
    Driveability complaint is usually opposite what you have: rpms drop TOO fast. In other words, the dashpot is ugly and unnecessary, but probably not your problem.


    Lube the throttle cable, check the Throttle body spring. Don't worry about TPS unless you have a code. Keep it simple.

    Sorry also for digging up this old thread. But I've been searching a lot about this problem with my car and I've learned a alot from the infos you have shared. I just want to thank you all.
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