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Thread: Tough Getting Idle speed correct with Idle Screw/TPS and IAC

  1. #1
    miniesean Guest

    Default Tough Getting Idle speed correct with Idle Screw/TPS and IAC

    I've been playing around with my Commander 950 MPFI for quite a while and have noticed that it is very difficult to dial in a good throttle position at hot idle so that the IAC position reads just over 10. For example, the IAC will show 200 at hot idle, meaning the IAC is wide open and that I need to open the throttle blades a bit. So I turn the idle adjust screw slightly and then the IAC will float down to 10. It then idles a bit too high. When I turn the screw like 1/16 turn back the other way to close the throttle blades slightly, then IAC starts floating back up to 200. Do you guys have this same issue? Does anyone know how to resolve this? It just seems that it is way too sensitive and that something is not right. It acts like the IAC has a very small range, but there must be something I am missing. Thanks for any help.

  2. #2
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    Enter zero in the first three "Minimum IAC Position" cells.
    What is your "Desired Idle" RPM (in Idle Air Control)?
    What is your "Max TPS for Idle" (in Engine Parameters)?
    Is the Fuel Map tuned in the idle area? Read about it here:
    http://forums.holley.com/showthread....e-Tuning-Notes

    Ensure the idle speed screw is set to achieve an IAC position of around 5-10 counts at hot idle.
    Ensure the spark plug wires (or any other high voltage wiring) aren't too close to the IAC motor/wiring.
    IAC TEST: When turning off the engine, watch the IAC pintle; it should fully close, then open halfway.
    If the idle speed screw is unscrewed too far, the engine is inhaling air from an additional source - vacuum leak.

    Which software and firmware versions are you using?
    Key-on/engine-off, click the "About" tab, then on the "Version" screen.
    The latest software version is 3.0.7 and firmware is 3.6.
    The ECU's firmware can only be updated by sending the ECU into Holley.
    The software can be updated by downloading it here:
    http://www.holley.com/TechService/Li...#FuelInjection ("Commander 950 Software")
    Check to ensure that your software version is compatible with your firmware version:
    1.xx = 1.xx
    2.xx = 2.xx
    3.xx = 3.xx
    Last edited by Danny Cabral; 01-21-2011 at 06:35 AM.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  3. #3
    miniesean Guest

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    I have version 3.0.7 and Firmware Version: 3

    Looks like I need to upgrade the firmware. Can I get this from Holley's website?

    My first 3 minimum IAC positions are: 10, 10, 10

    Desired Idle RPM is: 825

    My camshaft is 220/230 duration at .050. It's a hydraulic roller sbc.

    My max TPS for idle is: 32.

    Idle TPS is around 26-27.

    My fuel map at idle right now is the same fuel numbers for any idle position. Looks like this needs to be changed.

    I'll look at making the modifications you've talked about in your posts, including the min IAC positions to 0 and also the Fuel Map.
    In the meantime, based on this info, is there something obviously incorrect that's causing the issue? Thanks.

  4. #4
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    Quote Originally Posted by miniesean View Post
    Looks like I need to upgrade the firmware. Can I get this from Holley's website?
    No, the ECU needs to be sent in to Holley for the firmware upgrade. Only the new Holley EFI systems can update the firmware from an internet download.

    I'll look at making the modifications you've talked about in your posts, including the min IAC positions to 0 and also the Fuel Map.
    Yes, perform those adjustments and try these IAC PID Terms:
    Proportional: 22
    Integral: 18
    Derivative: 32

    In the meantime, based on this info, is there something obviously incorrect that's causing the issue? Thanks.
    Which wideband O2 sensor are you using and how is it wired?
    http://www.chevytalk.org/fusionbb/sh...hp?tid/256200/
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  5. #5
    miniesean Guest

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    I haven't had a chance to try the new settings yet because of too many hours at work this week, however I hope to by this weekend. Then I'll post the results. For now, in answer to the O2 sensor I am using: It is the wideband LC-1 from Innovate. I have it wired to the Holley harness. I bought a 3 pin weatherpack connector and from what I recall, wired just one of the analog outputs from the LC-1 to this 3 pin connector which I then just plugged into the Holley ecu harness. The rest of the O2 sensor wiring is per the LC-1 instructions (wired separately from the ECU)
    Do you know what differences there are between Firmware 3.0 and 3.6? thanks.

  6. #6
    miniesean Guest

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    Danny,
    I've tried the parameter changes you've recommended, but still seem to be having the same problem: cold idle rpm is too low
    To recap: I set the first 3 minimum IAC position values to zero. That seemed to help get a hot idle where the IAC would fluctuate between 0 and 10, which it never did before. I also have the fuel map tuned pretty well in the idle area (as you describe in posts). I also tried the new IAC PID terms. Engine will hot idle pretty steady at ~850rpm with IAC between 0 and 10. However, the following morning when I fire it up cold, it will idle too low (~600-650rpm) and IAC displays 200. Only way I can get it to idle up higher, to 950rpm where it should, is to set the throttle open more. However, then, at hot idle, rpm will be too high. I've even tried adding more and more and more fuel to the 'modifiers' table for cold running, but that didn't help. Seems like either the IAC is not really opening all the way when it says 200 or it is not really closing all the way when in says 0. It acts as though it does not have enough range. For your cold idle, what does the IAC go to? I imagine when you first fire it up, that it should go somewhere above 150, but not to 200, and then slowly retreat to around 5 as the engine warms up. Is there a good way to fully test the IAC? Could my issue have to do with having Firmware 3 and not 3.6? Any other thoughts? Thanks.

  7. #7
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    Quote Originally Posted by miniesean View Post
    For your cold idle, what does the IAC go to? I imagine when you first fire it up, that it should go somewhere above 150, but not to 200, and then slowly retreat to around 5 as the engine warms up.
    At 32°, my IAC runs at about 85% (new Holley EFI does IAC percentage, not numerical position), which is 170 numerical position. Then yes, it slowly decreases as the engine warms up.

    It seems like your IAC motor is defective. The ECU is trying to open it further to increase idle RPM but it won't open, that's why it's going to 200. Can you try another IAC motor? (C950 uses a Chrysler IAC - '00-03' Dodge fullsize truck.) TEST: When turning off the engine, watch the IAC pintle; it should fully close, then open halfway. Make sure the Coolant Temperature Enrichment isn't too rich (manually opening the throttle, leans out a rich condition and causes the engine to run better). What's the air/fuel ratio during this low RPM period?
    Last edited by Danny Cabral; 02-01-2011 at 05:25 AM.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  8. #8
    miniesean Guest

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    Ok, now we're getting somewhere. Thanks for your help so far. You are correct that there is something wrong with the IAC motor: either stepper motor's bad or signal to it is bad. I fired the engine up cold and watched the IAC. It starts out about half open (like it should) and is continuously moving back and forth slightly. At the same time, I'm watching what the ECU is commanding the IAC to do: the number is readily, but not too quickly moving up from ~100 towards 200. It get's to 200 and right about that time, the IAC has now moved all the way shut. IAC was slowly moving shut (all the while also slightly moving in and out) while the ECU number was steadily moving higher. The other test: when the engine is shut off, the IAC closes all the way (it's already basically there) and then moves to about half open.
    Next...I wanted to test whether it's a bad motor vs. something wrong with the electrical signal. There are 4 wires on that connector. With key on, engine off, ECU is commanding IAC to 100 and 2 of those wires are at 10.5V. The other 2 are zero volts. With engine running, all 4 wires have voltage signals that are all over the place. 3, 8, 6, 9 volts back and forth. I couldn't make sense of that. ECU at this point should be trying to drive the IAC to zero because the engine was running 2k rpm and IAC value on the ECU showed zero. I'm not sure what signal the IAC is supposed to see. Can you shed any light on this? Thanks.

  9. #9
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    Quote Originally Posted by miniesean View Post
    It get's to 200 and right about that time, the IAC has now moved all the way shut.
    I think I know what's wrong. It seems your IAC motor is wired wrong. There actually were some older Commander 950 systems that had the four IAC wires pinned wrong, caused the IAC motor to operate in reverse. This may be your problem. Look at the Wiring Diagrams for your application, in Appendix 10 of the C950 manual and see if your IAC is wired wrong. The PDF copy on Holley's website will allow you to enlarge the print to view it easier. If so, the IAC connector terminals are Metri-Pack 150 "pull-to-seat" terminals (if you decide to replace to terminals):
    http://whiteproducts.com/metripack-faqs.shtml (scroll down for illustration)
    http://www.holley.com/data/Products/...99R10149-7.pdf (C950 manual)
    Last edited by Danny Cabral; 02-02-2011 at 05:01 AM.
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS TW 11R 205 heads, 11.8:1 comp, TFS R-Series intake, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 160A 3G alternator, Optima Red battery, A/C, 100HP progressive dry direct-port NOS, Spal dual 12" fans/3-core Frostbite aluminum radiator, Pypes dual 2.5" exhaust/off-road X-pipe/shorty headers, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/2800 RPM converter, M4602G aluminum driveshaft, FRPP 3.31 gears, Cobra Trac-Lok differential, Moser 31 spline axles, '04 Cobra 4-disc brakes, '93 Cobra booster & M/C, 5-lug Bullitt wheels & 245/45R17 tires.

  10. #10
    miniesean Guest

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    It looks like there is something wrong with either the Wiring or ECU or electrical noise (noise as a possibility from what I read from other posts). I tried another brand new Holley IAC motor from my brother's kit which he just bought and had the same exact issue. I highly doubt 2 motors were both bad.
    So then I turned to the wiring and tried what I thought was the possible wiring mistake (according to the Holley wiring schematic), but that didn't make it work correctly either. When I performed the wiring change, the IAC motor opened up too much and let it idle at almost 2k rpm, while the ECU commanded it to go to zero.
    Mine original wiring is like this: The connector has, A, B, C, and D printed on it, in a row like that. Each letter corresponds correctly to the wire color as shown in the schematic, but the difference is that the schematic shows A, D, B, C as though that's how they are supposed to line up in the connector. So I tried wiring how the schematic shows them to line up: A, D, B, C,...and that is what didn't work. I even tried opposite: C, B, D, A. Didn't work. Then I tried some of the other things mentioned in other posts:
    1) I ground the ECU case directly to the battery
    2) I hooked up the O2 Sensor ground and power directly to the Holley ECU. Before I had only the analog output signal direct to the ECU and the power and ground were done separate.
    http://www.chevytalk.org/fusionbb/sh...post/last/m/1/

    After trying these things, nothing made any difference. Same issue. I'm stumped.
    Only other thing I can think of trying right now is a different HEI ignition module.
    I saw in this post that was claimed to help his issue:
    http://www.chevytalk.org/fusionbb/sh...hp?tid/211246/

    I'll try this and report back, but any other thoughts or suggestions?

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