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Thread: Idle's beautifully ... if I hold throttle to desired idle ... what's going on?

  1. #1
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    Default Idle's beautifully ... if I hold throttle to desired idle ... what's going on?

    I've been screwing around with the VE (lower area), timing, cracker and idle tables and, though the car will idle nicely all the way down to 700 RPMs (big cam, supercharger, LS7 Stroker, 2Bar MAP Sensor, COS5, SD mode), if I take my foot completely off the pedal, it will dip on down below 400-500 RPM's and die. This difficulty occurred after switching to the 411 PCM. The 2002 PCM solved my RPM over-rev issues and no longer kills the transmission, but just getting it to crank initially was an issue. I have non-sensical values I had to place for Injector flow rates to get it to crank and run. It runs strong now. But, this idle thing ...

    Any ideas what tables should I be massaging to overcome this?

    It won't settle out at the Desired Idle values I give it. What is going on?
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  2. #2
    Joe (Moderator) joecar's Avatar
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    Post a log file and the tune file.

  3. #3
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    Two Logs with different Parms and a tune I just uploaded where I increased Base Spark down low.
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  4. #4
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    Default Tune and 2 Scans

    Tune and 2 Scans
    Attached Files Attached Files
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  5. #5
    Joe (Moderator) joecar's Avatar
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    In your log 0224 I see several things:
    - MAP is high at 86 kPa when TP is steady at 7.5%... what cam specs do you have (intdur/exhdur lsa adv)...?
    - MAP flucuates while throttle is steady, I don't see IAC steps, but it is fluctuating too much.

    What intake manifold do you have...? Do have any vacuum/air leaks...?

  6. #6
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    The TP is 0% when the pedal is not pressed. Remember, I have to hold the throttle open slightly, for it to stay cranked. That's why you see a Throttle angle. I think it may even be off-idle.

    It idled the same place (800-900 RPMs, zero TP) on the 98 PCM and tune without cutting off.
    I don't think I have any vacuum leaks

    Also, remember, it wouldn't stay cranked the first time I loaded my tune after the PCM swap. I finally got it to stay cranked, but I can't take my foot off the accelerator pedal. Otherwise, it ran very strong.

    I have the LS7 Intake Manifold.

    Additional info: also, it cranks right up the first time, every time, cold or hot. But, I have to hold the throttle down slightly to maintain engine RPM at idle speed.

    Competition Cam:
    Gross Valve Lift: .623 .623
    Duration @ .006 Tappet Lift: 289 305


    Installed Specs:
    Duration @ .050 239 254
    Lobe Lift .367 .367
    Lobe Separation 115

    Thanks for your responses, joecar.
    Last edited by Black LS1 T/A; May 10th, 2017 at 10:07 PM. Reason: Cranking info added
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  7. #7
    Joe (Moderator) joecar's Avatar
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    ok, we may have to go thru the idle tutorials...

  8. #8
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    OK. The car is not inspected yet, so I can't drive ... just idle in my driveway.
    I'm getting a 10-day tag Monday, so I can take it to a tuner who says he is willing to tune with EFILive, and inspect the car so I can drive it. But, I need to time the 10-day tag where I can drive it a few days and still get it to him to iron out kinks before inspection. I was hoping I could get as much resolved as I can before I take it to him.

    Every tuner around here uses the other package. I don't know why it's become entrenched in the market here. :(
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  9. #9
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    I got it to idle without shutting off.
    Adjusted quite a few idle parameters, so I can't say what by itself may have done it.
    I also adjusted Injector Min Pulse width and Small Pulse adjust
    Old numbers with 422 Iron Block
    10.84 @ 124 MPH, 1.57 60\'
    549 RWHP / 757 RWTQ
    I'd rather be blown ... AND stroked!
    Now: 441 CID (Corevette 427) , ATI Procharger D-1SC Supercharger

  10. #10
    Joe (Moderator) joecar's Avatar
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    Post the before and after tunes, lets have a look.

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