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What's Your Idle Speed?

This is a discussion on What's Your Idle Speed? within the General Help forums, part of the LSx Technical Help Section category; Originally Posted by Naaman But it does affect the idle speed, right? If I'm getting a tune, what are my ...

  1. #61
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Naaman View Post
    But it does affect the idle speed, right? If I'm getting a tune, what are my options generally? I heard of "street tunes" and "dyno tunes"... what else is on the menu if I have to go that route?
    Yes it probably will affect the idle speed, because opening the throttle blade is assentially creating a vacuum leak and raising the idle. The opposite should lower idle.

    The computer does the same thing with the IAC step motor. Opening it creates a vacuum leak and raises idle, and vise versa. That's how the computer controls the idle.

    If the scew is having no affect, and you believe the tune is commanding a lower idle than what you have. Then I would suspect you have a vacuum leak somewhere.

    As far as tunes, on a mild car a mail order from Frost is the cheapest way to go and he does a nice job. He'll work with you on things as well, like where you want your car to idle for instance.
    Some people like tuning on the street with various loads if you have your own tuning software, others prefer to use a dyno and get it done quicker, albiet more expensive though.

    I have my own software, so I "street tune" as you call it with alot of logging, driving, various loads etc....I'll use the track as a dyno to find the WOT AFR the car likes, then call it done.
    I've only used a chassis dyno for giggles if the opportunity presents itself. Otherwise I don't bother with them. Most of the time we use an engine dyno before it even goes in the car.
    It's part personal preference and part what you have available to you.

  2. #62
    Senior Member Naaman's Avatar
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    Ah, awesome reply.

    I'll probably get my tune done locally, since I'm not sure I want to muck around with pulling the ECU out, and to avoid downtime (it's my daily).

    BTW, how do I check for a vacuum leak?

  3. #63
    Moderator Cutlass's Avatar
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    Quote Originally Posted by Naaman View Post
    Ah, awesome reply.

    I'll probably get my tune done locally, since I'm not sure I want to muck around with pulling the ECU out, and to avoid downtime (it's my daily).

    BTW, how do I check for a vacuum leak?
    Listen for air sucking sounds with the engine running, which is sometimes somewhat difficult on this. You can also spray carb cleaner on some suspect areas with the engine running. When you spray a vacuum leak with carb cleaner the idle will change up or down.
    But I'd start with visually inspecting the PCV hose for a leak. its a common leak source.

  4. #64
    Senior Member Naaman's Avatar
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    You said carb cleaner... I assume MAF cleaner or TB cleaner will work just as well, right? (I already have those on hand).

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    Moderator Cutlass's Avatar
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    Yep both should work. Both are flammable I think so either should work.

  6. #66
    Senior Member Naaman's Avatar
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    I just tried spraying carb cleaner around the engine and the lines. No change in idle speed...

    One thing I've noticed is that someone performed the free ram air mod on this car before I bought it (cut out the plastic thingy under the air filter). Can things like this (free mods) raise the idle?

    What else could it be? I might just try getting it tuned soon...

  7. #67
    Senior Member Naaman's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    I tried it with out the screw and it would still idle @ 1000 rpm. Also it caused the spring to get stuck and not respond to the pedal because it is to far down.

    For shits and grins I threw back the non ported TB and still had it idling at 1000 rpm.
    So, I noticed you mentioned that some 98s have the Corvette cam in them... I didn't know there was a difference in cams, although that would explain differences in the power curve and suchlike.

    Is there a resource that can break down the cam distribution by VIN? I'd be interested to know if mine has that cam.

    Is the C5 cam more aggressive? The previous owner gave me a dyno of his car (I believe it was after the cat-back was installed). 275 HP. Don't know the type of dyno used or the altitude/temperature etc...

  8. #68
    Insurgent Hunter dethinboots's Avatar
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    hmmm

    My gto only idles at higher rpms like that after an internal seafoam treatment.
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  9. #69
    Spaz is My Mentor SMWS6TA's Avatar
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    Quote Originally Posted by Naaman View Post
    So, I noticed you mentioned that some 98s have the Corvette cam in them... I didn't know there was a difference in cams, although that would explain differences in the power curve and suchlike.

    Is there a resource that can break down the cam distribution by VIN? I'd be interested to know if mine has that cam.

    Is the C5 cam more aggressive? The previous owner gave me a dyno of his car (I believe it was after the cat-back was installed). 275 HP. Don't know the type of dyno used or the altitude/temperature etc...

    I'm not sure if the dealer can look up by vin what cam you have. It was just a short few that had them installed due to a shortage. From what I read on some of the other forums it was minimal gains.

    On the dyno paperwork does it state anything like Mustang Dyno or Dynojet?

  10. #70
    Senior Member Naaman's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    On the dyno paperwork does it state anything like Mustang Dyno or Dynojet?
    I'm not sure. I'll have to look this up when I get home. I thought 275 was kinda low, but it works out to about 315 bhp assuming 15% losses. Factory rating was 305... as if you didn't know already.

  11. #71
    Senior Member Naaman's Avatar
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    Quote Originally Posted by SMWS6TA View Post
    I'm not sure if the dealer can look up by vin what cam you have. It was just a short few that had them installed due to a shortage. From what I read on some of the other forums it was minimal gains.

    On the dyno paperwork does it state anything like Mustang Dyno or Dynojet?
    Quote Originally Posted by Naaman View Post
    I'm not sure. I'll have to look this up when I get home. I thought 275 was kinda low, but it works out to about 315 bhp assuming 15% losses. Factory rating was 305... as if you didn't know already.
    Okay, I have two dynos both done on the same day. The first one maxes out at 273.1 horsepower (doesn't say the rpm, but it looks like they backed off at 5500). The max torque for that run was 294.5 lb.ft. Again doesn't say the rpm but it looks like mid 4000s.

    The other dyno shows a max power of 278.5 at what appears to be just over 5600 with a torque peak of 298.6 at what looks like 3950. This torque curve on this second dyno looks very choppy as if they were not measuring at WOT or something (or maybe not... I don't know).

    The dynos are from "Turbo Technology Inc." I cannot determine whether these were done before or after the Magnaflow cat-back.
    Last edited by Naaman; 06-15-2011 at 10:57 AM.

  12. #72
    Slow'er'Ass Mr. Luos's Avatar
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    As for the whacky RPM readings....could be the dyno operator(s) or the equipment. Several times with my guy I had issues getting an accurate RPM reading because of the coil location mixed with the ground location.



    I could be wrong here....but it sounds as though there is an adjustable throttle body blade on this car.
    If it is stock, there is no way to adjust it without drilling a hole in the blade itself.
    I would think a tuner that is buttoning up a tune in person would know to check the blade position along with his idle tuning.

  13. #73
    Senior Member Naaman's Avatar
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    Well, I just swapped to a ported (stock) throttle body. I removed the one on the car and replaced it with one ported by S2 performance. The engine is much more responsive, and I can feel more of a pull throughout the power band. I also played with that little screw that seats the throttle cam to try and lower the idle. I could not get it to go lower without the pedal sticking, so it stays at 1000 rpm.

  14. #74
    Moderator Cutlass's Avatar
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    If the pedal sticks when you back the TB screw all the way out, then the blade isn't centered in the TB. A blade that isn't centered, will cause a high idle. Thats what I found on mine.

  15. #75
    Senior Member Naaman's Avatar
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    The plot thickens

    Is this a machining issue or just a screwdriver and micrometer issue? Or maybe it can be eyeballed (?).

    Both throttle bodies I've used have the same idle.

  16. #76
    Spaz is My Mentor SMWS6TA's Avatar
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    so how can I center it? It looks flush and center to me, I see no gaps with a light on the back side. also it had the same idle with the stock TB.

  17. #77
    Moderator Cutlass's Avatar
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    I back the idle stop screw all the way out so the TB can close completely. I then loosened the screws holding the blade to the shaft. There's enough play in the screw holes to make adjustments.
    With the blade screws loose, I opened and snapped close the TB a few times. That motion moved the blade around and centered it. I then tightened the blade screws up and rechecked it. It didn't bind anymore, so I knew it was centered. I bumped the idle stop screw gently up against the throttle lever and reinstalled the TB on the car.
    Using a scan tool, my IAC counts (how far the Idle Air Control motor is open) were at about 40. Previous to this repair, the counts were at ZERO (meaning the IAC was completely closed).
    Thats when I knew I solved my high idle.

  18. #78
    What Would Earl Do? Vexzer's Avatar
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    Quote Originally Posted by Cutlass View Post
    loosened the screws holding the blade to the shaft
    Be sure they can't come loose. If the motor eats them it won't like the taste, and can't spit the back out. I thought these are edge-punched in place so they can't come loose. Good luck.

  19. #79
    Moderator Cutlass's Avatar
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    I was definitely worried about that also. I made sure they wouldn't come loose...but I think I may go recheck them this weekend to make sure they are still ok. Its been a few years now since I've checked them.

  20. #80
    Senior Member Naaman's Avatar
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    Quote Originally Posted by Cutlass View Post
    I was definitely worried about that also. I made sure they wouldn't come loose...but I think I may go recheck them this weekend to make sure they are still ok. Its been a few years now since I've checked them.
    If the most complex thing I've done on my car is swap the throttle body, what do you think my chances are of balancing the blade successfully without ruining my motor? Should I get help on this or is it "safe" to do on my own?

    It seems pretty straight forward, but... given the possible risks...

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