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Thread: Bad Idle - I found my solution...

  1. #1
    Join Date
    Jul 2018
    Posts
    3

    Default Bad Idle - I found my solution...

    I've been struggling with a bad cold idle and occasionally bad warm idle since installing Atomic EFA on my 260hp Gen 1 small block Chevy. The idle was going up and down and sometimes stalled. The clue I needed came from an earlier post from a MSD tech who said mechanical timing can work against the IAC causing instability in the idle speed. He later said that allowing your Atomic EFI control your timing would help. That got me wondering if my mechanical advance springs were too light? The theory being that a little IAC opening might spin up the timing advance causing even more RPMs (timing advance increases RPMs) with the aftermath being less IAC causing less advance driving an oscillation between slow to fast to slow idle. I opened up my distributor, and sure enough, I had one very light and one medium spring in there. I replaced the springs with a pair of new medium silver springs. Then I checked the timing. My initial timing moved from 13 degrees to 4 degreed and timing at 3,000 RPMs was unchanged at 30 degrees. This tells me that I was getting a bit of mechanical advance at my 850 RPM idle. I increased the base timing to 7 degrees which got me 32 degrees at 3,000 RPMs as recommended by my crate engine builder(GM). The stiffer springs were immediately noticed upon cold start, much much more stable. I have my IAC set to zero at about 850 RPMs as this thing has a manual transmission. The warm idle took a few minutes to smooth out even with the IAC at zero... I'm assuming the timing changed the fuel map a bit. The next day, I drove to work. Cold idle was fine but I started using the AC... and so the EFI needed a little time to adjust the worm idle to prevent stalling at stop signs. (I have not yet hooked up the AC kick up wire.) All was fine by the time I got to work 20 minutes later.

    So all of the above is a long winded way of saying... light mechanical advance springs can cause unstable idle.
    That sort of problem is not the fault of the Atomic EFI.

  2. #2
    Join Date
    Jul 2018
    Posts
    3

    Default

    Locked out the distributor today and wired in the Atomic timing control. The idle during test drive was great.

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