Page 1 of 2 12 LastLast
Results 1 to 10 of 12

Thread: Idle RPM whilst coasting

  1. #1
    New Member
    Join Date
    Feb 2005
    Posts
    6

    Default Idle RPM whilst coasting

    Hi All, This is my first post.

    I've been reading here for a while and there is some great info on here.

    I'm building an AC Cobra with an LS1 under the hood. I also help out a bit with some other guys LS1 powered Cobras.

    One thing we've noticed with the LS1 is that when you are coasting along at speed and you release the accelerator and press in the clutch the idle sits up around 1200 RPM. Once you slow down and stop it drops back down to normal 800 RPM or so. I figure this is a function in the tuning to make the car smoother to drive on the road when shifting gears etc. By the way it dropps of when you slow down to a certain speed it makes me think it's something the ECU is doing with the IAC relative to the Vehicles speed sensor.

    In a lightweight 1100KG Cobra this is down right anoying since that 1200RPM is almost enough revs that you don't slow down when you back off the throttle. It means you have very little engine braking especially when the motor is supercharged and makes 550RWHP.

    Is this a feature that can be disabled or a table that can be adjusted? It would be good if the idle stayed the same regardless of the speed you're doing as it would make the car feel a lot more natural.

    Cheers

    Michael
    Cheers

    Michael

  2. #2
    Lifetime Member GMPX's Avatar
    Join Date
    Apr 2003
    Posts
    13,148

    Default

    Table B4309 will be your friend. It holds the IAC out above it's park position based on road speed, so also make sure your park position is not too high (table B4308).

    Cheers,
    Ross

  3. #3
    New Member
    Join Date
    Feb 2005
    Posts
    6

    Default

    Thanks Ross!
    Cheers

    Michael

  4. #4
    Lifetime Member jfpilla's Avatar
    Join Date
    Apr 2003
    Posts
    666

    Default

    Check one other thing. If the idle airflow is too high it will act like the throttle cracker and give you that cruise affect. I would lower the idle airflow value at the temp. it cruises and use the Cracker for finer adjustments.
    2003 red vert
    Mods:
    LS7 crate engine, wet sump, 24xx reluctor
    LPE 100mm MAF
    Vararam, cold air intake and bridge
    RPM Level 6/4L60e trans
    3.42 gears
    Yank SS3600
    1-7/8" AR headers
    Z06 exhaust
    470rwhp 437rwtq
    1/8th mi-1.526-60'-6.862-1/8th-@100.74mph

  5. #5
    Lifetime Member mistermike's Avatar
    Join Date
    Dec 2003
    Posts
    363

    Default

    I've kind of wondered what the logic of tracking road speed on the idle is, because my car does it too.

    Cobra Man, 550 RWHP in an AC Cobra? Probably on one of those low-reading Aussie dynos too. You're a sick individual :wink:
    That thing's gotta be like getting shot out of a canon. What kind of blower are you running?
    World's First Twin Screw Pontiac GTO
    2004 GTO. Blown H/C 408, stage 3 keyboard, billet tires
    2017 Chevy SS with dead hooker is spacious trunk
    2014 Chevy Cruze. MPG queen with my balls in spacious glove compartment.

    www.aussiemotive.com

  6. #6
    Lifetime Member jfpilla's Avatar
    Join Date
    Apr 2003
    Posts
    666

    Default

    mistermike, I'm not sure I understand what you're saying?
    To clarify a point. Idle only occurs when the car is stopped. As soon as it starts to move the Throttle Cracker takes over. If Idle Airflow is to high the car will cruise because the TC is additive to IAF. IAF is often called Running Airflow because of that affect, I think. This part of tuning can be frustrating, when tuning a big cam car, since it may be necessary to have some cruise, just as it's necessary to have a high idle.
    2003 red vert
    Mods:
    LS7 crate engine, wet sump, 24xx reluctor
    LPE 100mm MAF
    Vararam, cold air intake and bridge
    RPM Level 6/4L60e trans
    3.42 gears
    Yank SS3600
    1-7/8" AR headers
    Z06 exhaust
    470rwhp 437rwtq
    1/8th mi-1.526-60'-6.862-1/8th-@100.74mph

  7. #7
    Senior Member
    Join Date
    Dec 2004
    Posts
    124

    Default

    I changed both my IAC and IAC Parked values to 9.0 g/s for all values above 60C. The engine so smooth at idle it feels like a stocky if you ignored the lopey sound.

    I found that my IAC Parked values were set too high (at 10.0 g/s), which slightly elevated the revs by around 300-400rpm before settling at the normal idle speed of around 950rpm.

    BTW, I have a 224/224 110 lsa cam.

  8. #8
    Lifetime Member jfpilla's Avatar
    Join Date
    Apr 2003
    Posts
    666

    Default

    SSbaby, Did you lower the Idle Airfow values and Idle Airflow Parked at the same time? The reason I ask, is that 60C is a high IAT. Is it that hot there? If your IAT is not exceeding 60C the change in IAParked might not have done anything. Also, lowering IAParked should increase the aiflow.
    2003 red vert
    Mods:
    LS7 crate engine, wet sump, 24xx reluctor
    LPE 100mm MAF
    Vararam, cold air intake and bridge
    RPM Level 6/4L60e trans
    3.42 gears
    Yank SS3600
    1-7/8" AR headers
    Z06 exhaust
    470rwhp 437rwtq
    1/8th mi-1.526-60'-6.862-1/8th-@100.74mph

  9. #9
    New Member
    Join Date
    Feb 2005
    Posts
    6

    Default

    The blown Cobra belongs to a friend of mine. My motor is basically stock at the moment. The Blower on my frineds car is a Procharger and it's producing the numbers with surprisingly little boost (around 7-8 PSI). He's running a set of full house Nathan Higgins heads, a 224 cam, 55 pound injectors and 2 Bosch 044 pumps. It accelerates like youre going into warp drive and it's the scariest thing I've ever driven in my life.

    Here's the dyno sheet after the heads went on and it got a MAFless tune. Since then it's got a new CAI stup as the normal Cobra bonet scoop just couldn't flow enough air. It later made 552RWHP on a Dynopac dyno with the intake mods.

    Cheers

    Michael

  10. #10
    Senior Member
    Join Date
    Dec 2004
    Posts
    124

    Default

    Quote Originally Posted by jfpilla
    SSbaby, Did you lower the Idle Airfow values and Idle Airflow Parked at the same time? The reason I ask, is that 60C is a high IAT. Is it that hot there? If your IAT is not exceeding 60C the change in IAParked might not have done anything. Also, lowering IAParked should increase the aiflow.
    Yes, I changed the values at the same time.

    Trust me when I say that by doing the changes described it also eliminated the annoying symptom of an escalation in revs before settling to the normal idle speed.

    I thought the idle air values corresponded to ETC not IAT temperatures? :? In which case my ETC temps would approach 80C+ and would therefore be influenced by the changes I made.

    PS Sorry to hijack your thread LS1 Cobra.

Page 1 of 2 12 LastLast

Similar Threads

  1. Idle's good but fluctuates while coasting
    By ForcedC5 in forum General (Petrol, Gas, Ethanol)
    Replies: 22
    Last Post: December 17th, 2009, 04:54 PM
  2. Need help with coasting down to idle
    By stevedarman in forum Gen III V8 Specific
    Replies: 0
    Last Post: August 26th, 2009, 12:10 AM
  3. Stuttering whilst cruising
    By hquick in forum General (Petrol, Gas, Ethanol)
    Replies: 3
    Last Post: April 27th, 2007, 01:30 AM
  4. Idle in N whilst moving
    By daveb in forum General (Petrol, Gas, Ethanol)
    Replies: 11
    Last Post: September 2nd, 2005, 01:42 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •