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SBC idle surge hot or cold and sometimes engine stall when selecting a gear

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  • SBC idle surge hot or cold and sometimes engine stall when selecting a gear

    I have a 383 SBC with the new Pro-Flo 4 system installed. The system works great and the vehicle (truck) drives great and has awesome throttle response. The only problem I have is sometimes the idle surges between 700 rpm and 1200 rpm hot or cold. Sometimes when I put the truck in reverse or drive (hot or cold) the engine stalls. In all cases the engine fires right back up, rev the engine once and off I go. What adjustments to idle should I do to correct these problems.

  • #2
    Helpful things to know: Which kit? What cal are you running? How much vacuum at idle? What's IAC position at cold idle and then at warm idle? What's your Idle Spark setting? What's your Idle AFR set point and what is your Short FT at idle when cold and warm? Does something in particular trigger the idle surge?


    • #3
      Finally got around to driving my truck so I could get the requested information.
      I have kit #35770.
      I,m running cal# 5029. This the number the Edelbrock Tech had me run when he helped me set the initial tune.
      Vacuum at idle is -16.5 in park and -14.9 in gear with the engine at operating temperature on the tablet. I also run a vacuum gauge which is connected directly to the engine and I read 12" in park and 10" in gear.
      IAC at cold idle is 14-15% and warm idle is 5-9%.
      Idle spark setting is 19-22.
      The idle AFR set point is 13.9.
      Short FT at idle cold is -12 and warm idle is -1 to +2.

      I have found nothing in particular makes the engine surge. Sometime when you start the engine it will surge from 550 to 1,000 RPM. Sometimes put the transmission in gear will cause a small surge. Once I tapped the gas pedal in gear and the engine died. The engine restarted fine, I revved the engine a little, put the trans back in gear and drove away. The engine runs really good so any suggestions to fine tune the idle is appreciated.



      • #4
        Good info. I'd try increasing your base throttle angle a little more to get the warm IAC position to be 0-5%. Just to clarify, when you say surge, do you mean it oscillates between those two rpm points over and over? For instance, the engine is idling fine at 750 (BTW what is your target idle speed?) and then all of a sudden for no reason it drops to 550 rpm then shoots to 1000 rpm and repeats this cycle over and over? Or does it idle fine at 750, dip to 550 and then surge to 1000 without oscillating and then return to back to the normal 750 idle? It might be helpful to use the screen capture video procedure to log some run data - give it a read here:

        One thing to try - one time before you start the engine, in the app, go to the On/Off Options in Advanced Tuning and turn Idle Feedback off. When Idle Feedback is off, the IAC only follows its open loop base position and the ignition timing will hold your base idle timing value. Normally when Idle Feedback is on, the IAC uses closed loop feedback to either open or close to help control engine speed and the timing will also adjust rapidly as well. By turning feedback off, this should really help to stabilize the system. Try starting the engine with Idle Feedback off to see if it makes a difference. This is just a test to try - not intended to be a permanent change.

        I highly recommend capturing some log video. Will be much easier for us to help troubleshoot. Also, what are you cam specs? Pretty big difference between vacuum readings from our system to your gauge.


        • #5
          Thanks for the quick response. I'll will try your recommendations including the data logger. Target idle is 800 RPM. The surge is only at idle and gently goes between 550 and maybe 1000 RPM. But the surge will start when Idling fine at 750 then bounce between 550 and 1000. The engine did surge a little today nut not too bad. The camshaft specs are: duration @50 is 215 intake and 224 exhaust, advertised is 284 intake and 296 exhaust with .470 intake lift and .490 exhaust lift, I'm also running 1.6 rockers, lobe separation angle is 108 intake and 116 exhaust. Once I make the above adjustments I'll write back.


          • #6
            I have lots and lots of questions but they'll all be answered once you supply us with a video log.


            • #7
              I emailed two videos, one with the engine cold and one with the engine at operating temperature. In the very first part of the operating temperature video the engine is surging a little, then settles down. Let me know what you think when you see the videos. Or if you don't see them also let me know. Thanks.


              • #8
                Saw you vids. Did see that short glimpse of idle surge at the beginning but being that it's just the tail end of it and it settles right back down, it's pretty hard to see any real cause and effect. Regular idle deviation is +/-50 rpm and you look to be in that range when warming up but it does seem like your idle gets a little more erratic once fully warmed up. Did you try turning idle feedback off to see if it changes anything? I'd also maybe think about doing a very thorough vacuum leak check. We recently had a strange idle surge problem with one of our R&D vehicles and it wound up being a very small vacuum leak.

                One other thing to try that I don't anticipate making a big difference is to update your E-Tuner 4 app to the latest version and then to update your firmware to v53. You should be able to just update the firmware without making any other changes and or having to reload your cal.


                • #9
                  The next time the engine surges I'll try and get a longer video of it. I have not tried turning off idle feedback but I will. I did open the IAC valve a little and got the IAC to 0-4. I was thinking of checking for vacuum leaks so I'll look for this as well as update the E-4 Tuner app and firmware. Thanks.