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Rough Running 1600-2000 rpm at Light Throttle Regardless of Gear

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    Rough Running 1600-2000 rpm at Light Throttle Regardless of Gear

    1992 EX automatic, 148,000 miles, stock. No codes. I installed new plugs after I purchased it at 145,000 miles.

    For a while, I thought it was just rough roads, but I've come to realize that the engine runs a little rough at light throttle (just barely pressing the accelerator) at about 1800 rpm regardless of what gear the transmission is in, whether I allow it to shift itself, or deliberately keep it in particular gear (1 and 2). If I deliberately raise the speed slowly, I can feel it start to get rough at about 1600 rpm and smooth out again at about 2000. I don't feel it at heavier throttle settings or as the engine coasts back through these speeds with my foot off the accelerator. Resistance range of the throttle position sensor seemed OK, but I swapped another one in because I had it available - no change.

    Now that I've typed this, I realize I haven't tried it in reverse or checked if it runs rough at that speed in neutral. I'll try that in the next couple days. That should be too low a speed for the IABs to kick in, but I'll check this as well.

    I think I have another EX ECU (ECM) around from my wrecked 93 EX that I can try.

    Any thoughts?
    90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
    08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

    #2
    Distributor. First thought I had anyhow.
    ......father in law has it back again. Time to shine

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      #3
      Originally posted by cb7 calling View Post
      Distributor. First thought I had anyhow.
      I didn't think of that because it seems to work OK at other speeds, but it is chock full of sensors (I still think of distributors from my old 60s and 70s GM products). I have a spare one of those around as well. I may try to hook up my Heathkit oscilloscope to look at the consistency of the spark from the coil.
      Last edited by Fleetw00d; 08-12-2015, 12:24 AM.
      90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
      08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

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        #4
        A bad igniter will cause missing at certain rpm ranges. Take off your distributor cap and check for oil on the magnets/igniter.

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          #5
          egr
          COUPE K24

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            #6
            ^yes! Good call, it'll obviously yield a code, but disconnect the egr valve from the harness and from vacuum and see if it continues. I had clogged egr ports on my old 93, disconnected the egr valve and the lower rpm range was smooth again.

            Comment


              #7
              Originally posted by '93CB7Ex View Post
              egr
              Thanks, that's probably the easiest thing to try. I haven't cleaned the passages in this one.
              90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
              08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

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                #8
                any vacuum leaks?

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                  #9
                  I've seen a couple Honda distributors start with rpm specific hiccups before they quit. Now they are usually fast hiccups, like one or two jumps 2800 ish.
                  ......father in law has it back again. Time to shine

                  Comment


                    #10
                    Originally posted by '93CB7Ex View Post
                    egr
                    Bingo! Plugged the vacuum line this evening before running to get Friday night pizza. Smooth all the way through the rpm range; seemed to idle smoother as well (isn't EGT closed at idle?). Rough running likely because one or more ports are more blocked than others?

                    The question now is do I clean the valve and ports or block off the valve? I will probably opt for the former; I like things to work the way they are supposed to.
                    90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
                    08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

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                      #11
                      Take it off and pressure test it first. They're not cheap, and cleaning is always worth it. Yes the EGR is closed at idle. It opens at 1800 if I remember right

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                        #12
                        It seems like it's always the egr. Though I have never seen that problem in person.
                        ......father in law has it back again. Time to shine

                        Comment


                          #13
                          Originally posted by F22Chris View Post
                          Take it off and pressure test it first. They're not cheap, and cleaning is always worth it. Yes the EGR is closed at idle. It opens at 1800 if I remember right
                          Pressure test the valve to make sure it's not leaking? If leaking, wouldn't it leak exhaust out (higher exhaust pressure than intake)? If so, would it really affect how much exhaust is going into the intake manifold? Or leaking into the vacuum line that actuates it (too much exhaust recirculating)? Just asking. I think I have a spare EGR valve around.
                          90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
                          08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

                          Comment


                            #14
                            Originally posted by fleetw00d View Post
                            Pressure test the valve to make sure it's not leaking? If leaking, wouldn't it leak exhaust out (higher exhaust pressure than intake)? If so, would it really affect how much exhaust is going into the intake manifold? Or leaking into the vacuum line that actuates it (too much exhaust recirculating)? Just asking. I think I have a spare EGR valve around.
                            If it doesn't hold pressure, it will stay closed at all the rpm ranges. Ha, it's funny saying this, but suck on the nipple and plug it with your finger and see if it stays.

                            Comment


                              #15
                              Originally posted by F22Chris View Post
                              If it doesn't hold pressure, it will stay closed at all the rpm ranges. Ha, it's funny saying this, but suck on the nipple and plug it with your finger and see if it stays.
                              I don't think it is staying closed. With vacuum disconnected (staying closed), the CEL came on after a short bit of driving. With everything connected correctly, no codes and it runs rough indicating that it is opening. While I don't mind sucking on nipples and plugging certain things with my finger, I think I'll use a vacuum pump to check it.
                              90 LX 4dr 5 spd 396,014 (sold 1/1/2022) - MRT: http://www.cb7tuner.com/vbb/showthread.php?t=201450
                              08 Element LX FWD AT 229,000 - MRT: fleetw00d : 2008 Honda Element LX - CB7Tuner Forums

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