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3 Questions: Lower Idle at stop light - sometimes, Spark Control, right map?

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  • 3 Questions: Lower Idle at stop light - sometimes, Spark Control, right map?

    Hello everyone,
    First time caller, long time listener. I have 3 questions, but first my specs:

    1970, 351W, Edelbrock performer RPM intake, FMX auto transmission, Estreet2 EFI, Edelbrock electronic distributor, dual electric fans hooked up through a different control...beefy alternator.
    Cam - Not sure but it has a 302 timing. Vac is at 17 so I think it's stock or super mild. The car was an older restoration which tells me that back in the day they didn't have stock replacement 351 cams.

    MAP 36005V21
    AFR - 14.1, 14.1, 13.3
    Pump Shot 6%, 2 sec
    Idle set to 750
    Vac - at least 17
    Cold Start at 8% (not that it matters)
    Timing - 18 initial, 1200, 34.00, 3000 RPM. 6 vac advance.

    1). Car starts are runs decently (after months of tweaking), but every so often (1 in 6 times) when I stop at a stoplight the idle goes to 670. Most of the time is goes to 750 which is where I set it to. Any idea why it would act this way? I'd prefer to set my idle lower, but the 1 in 6 lower RPM at a stop has me worried she'll stall.

    2). I really like the Edelbrock electronic distributor. I manually set it to 12 BTDC then followed the instructions. I set the app to 18 BTDC with all the settings above, but it chooses to idle at 21-22 BTDC. Any idea why it does that? I assume that it's choosing the best timing...kind of like HAL5000 in 2001 A Space Odyssey - self actualized.

    3). Do I have the right map? For some reason I think there is no setting for 351 so maybe I chose the 350. In the past I bounced between stock and mild cam. I think mild cam ended up a bit better but I've tweaked so many settings over 18 months that I can't remember.

    Lastly, are there any settings that you would recommend I modify based on your experience?

    P.S. This forum is very good. These things love a lot of initial timing. I fought the power on it (to stay at 12) until the power won and made me adjust for smooth idle. The ground strap on my spark plugs tells me my total timing is too much, but 34 should be correct.


  • #2
    I believe you set the idle speed with the IAC covered, turn off the car ( this sets the TPS )...I think you set that first idle speed 50 RPMs higher then what your try to set it to.

    The timing control is most likly adding some vacuum advance.
    At 43,861 MPH Elon Musk now owns the fastest car in this Galaxy


    • #3
      Thanks Bite me. I reset the system and loaded the map for the stock cam. I also properly adjusted the idle but dropped it lower which I prefer. She runs okay but I need to put more miles on for the computer to learn.

      I remember why I went with the mild cam option - the idle AFR adjustment reads 25% in stock and it was closer to 10% in mild cam. I'll let it run awhile over a few days and report back.

      Reference vacuum advance - You were correct. I dropped mine down to zero and my initial timing is 18 degrees BTDC.


      • #4
        The vacuum advance helps with fuel economy and idle control. I would set it to at least 5 degrees, most people run 7-8 depending on the camshaft. Your total timing will be dictated by the octane of the fuel, compression ratio and combustion chamber design. Listening for detonation and reading the plugs is the best way to determine the total timing the engine wants.

        You mentioned the AFR correction is 25%, but didn't state plus or minus. You can go into fuel modifiers and add or subtract fuel to bring the correction percentage down into single digits. Your AFR targets are fine.

        When you set the idle speed, cover the IAC hole and then set the idle on the throttle body screw. After you have set your target to lets say 800, then go into the tablet and set the Target Idle speed to 50 rpm less, which would be 750. Also the adjustmens, you may need to calibrate the TPS if it doesn't read 10 at idle.

        You can try the both maps and see which runs better. With the idle vacuum being over 15", it should be on a stock cam map.


        • #5
          Thank you for the reply. My vacuum is usually around 18". I set the vac advance back to 6.

          My AFR correction was -25%ish with the stock cam chosen and single digits with mild. I reset and double-checked how I set the idle - all good. As you suggested, I played with the fuel modifiers (idle -10 to 20) to get the correction to single digits, but my car started stalling at stops (frightening in Carlisle, PA traffic this time of year - Ford Nationals!). My initial problem was occasional low idle when stopping and she's still a problem. She'd idle fine from a cold or hot start but once I start driving and hit a stop light she'd drop down 75 or so rpm (about 1 in 6 times). Sometimes she would bounce back up, sometimes not. I think editing the fuel modifiers made it worse. Ideally I have her set to idle at 700 rpm.

          The AFR correction was (-) so I used the modifier correction (-).

          I reset self learning and adjusted the AFR to 13.9, 13.9, 13.3.

          I'm pretty sure my car gets pretty lean when I stop then it shows rich. Perhaps that's normal.

          What is the big difference in the software between mild and stock?


          • #6
            Follow Up:

            I ended up going back to the mild cam base map instead of the stock base map. I also change the idle back to 750 instead of 700. The AFR correction is single digits now. She still occasionally drops the idle to 675 when I get to a stop light but the car doesn't stall. The idle is higher than I prefer, but she's driveable. She still runs a bit rough until I hit 170 degrees but again, she's driveable.


            • #7
              You can make adjustments to Cold Start Enrichment under the Advanced Tuning section. You can add or subtract fuel from the warm up area. I suggest subtracting 10% and see if that helps. Don't make small changes like 1-2% as you can't really feel that until you get it dialed in. If 10% improves it, then bump it to 15%. If subtracting 10% makes it worse, then go the other way and add 10%. It is a bit of trial and error to dial it in for your engine combo.