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Thread: JDM D15B Swap Idle Surge

  1. #1

    Default JDM D15B Swap Idle Surge

    I am experiencing an engine surge during warm idle. I have a JDM D15B engine swap into a 1988 CRX. I am using a P28 ECU OBD1 (of course). I have replaced the EACV, Fast Idle Valve, and have made sure that both thermoswitches are covered by coolant. I still have an idle surge. When I sart up cold the engine idles and warms just fine. As soon as I hit the throttle, it begins to surge between 1000 and 1500 rpms. I have exhausted all options except a different ECU. I have reviewed other surge issues and feel that I have covered the typical reasons for an idle surge. Any suggestions?


  2. #2


    so, you bled the coolant, changed, the iacv... do you have a vacuum leak maybe?
    idle surges piss me off.
    ~ 2001 Silverstone Metallic Honda S2000

    Quote Originally Posted by EXCellR8 View Post
    my little rod broke off

  3. #3


    I have the same problem with my h22.. I have yet to figure it out yet.. But I haven't fucked with it that much..

    Let me know if you figure it out so I can try it.. Or if I figure mine out ill let you know

  4. #4

    Default Update: Idle Surge Problem

    Pesky idle surge... Well, I have no ECU codes at all, coolant is topped off, checked for vacuum leaks, none found that seemed apparent.

    Some other folks with similar idle problems have had forum responses that suggest the TPS. I will look into this...

    When I start the car it idles fast, then slows down to a normal RPM after warming up. However, normal rpms are around 1000 rpms with the idle adjustment screw completely closed. (Vacuum leak?) This indicates to me that the Fast Idle Valve is operating properly. If I unplug the IACV the rpms drop approximately 320 rpms, as they should. This tells me the IACV is operating properly. When I open the throttle, the car begins to exhibit the idle surge when the throttle returns to the closed position. Thus, I believe the problem lies with the throttle body, TPS, or ECU.

    My approach is to replace the throttlebody and TPS first. It is the cheapest part off Ebay to replace and I think that if the throttle blade shaft or return spring are worn or bent, it may produce the vacuum leak that could cause the problem. If replacement of the throttlebody and TPS doesn't solve the problem, I will find another ECU. If another ECU does not resolve the problem, I will take another close look at the wiring to the TPS and IACV. I have alread inspected the wiring for proper connection, but a bad male/female socket connection could be a cause. Outside of these actions, I don't know how to fix the surge.

    I will have the replacement TPS later this week. I will keep readers informed of the result, since many others have this same problem. The beauty of a car problem like this is beating it in the end.

  5. #5

    Default Follow-up: Surge Resolved

    For those who correctly suspected a vacuum leak. You were correct. The vacuum leak was caused by a small gap between the butterfly blade and the throttlebody itself. There was enough of a gap to allow enough air into the plenum, the IACV would try to compensate, then a pulsation feedback would start between the vacuum leak and the IACV. One cannot see the gap between the blade and TB unless you have a light source behind it when it is closed. Very sneaky.

    I had a spare TB that closed properly. I installed it and the surge was gone. So, add to the list of possible vacuum leak sources the TB B-fly Blade.

    Thanks to all that responded, and I hope this helps folks out there solve this nasty problem.

  6. #6


    wow.. sneaky.. nice to know and glad you got it fixed
    ~ 2001 Silverstone Metallic Honda S2000

    Quote Originally Posted by EXCellR8 View Post
    my little rod broke off

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