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Thread: IAC Position Changes

  1. #1
    Join Date
    Apr 2016
    Location
    Indianapolis, IN
    Posts
    5

    Default IAC Position Changes

    Hey All. Could really use your help with an issue I'm having.

    Specs:
    LS3 engine close to stock, cam changed to a 230°/234° .612"/.598", using L92 heads that have been milled .015", throttle body changed from 90mm to 95mm throttle body. The car is an automatic with a 4L80E.

    Back story:
    Last year I changed the throttle body from a 90mm to a 95mm around 6/27/20 (part number 112-585). There wasn't really a reason to change the throttle body, it was more for aesthetics and the other one came from someone else that I had no previous knowledge on. When I changed the throttle body I had a bunch of sensors go bad. MAT sensor was the main one. When it went out I had no idea, and the car wouldn't run right and kept stalling all the time, which was strange for an automatic car. I noticed the main reason it was stalling was when I tapped the gas then quickly got off. An example would be like when you are at a stop sign. The person in front goes. You give the car some gas to move up, then let off. This is when I'd stall.

    Before the throttle body change, the Base Fuel Table had a lot of drive time on it, and I had never had this issue before. I took it to a Holley dealer and they looked over the car and found the MAP sensor to be bad. Once changed, the car seemed to be fine again. But something was different now. But it was November by this time, and I had to put the car up because winter was coming soon.

    Issue:
    I started the car in February to let it idle and get some heat into it. I noticed when I was looking at the sensors that the IAC Position when hot (200°F) read at ~20-22%. I knew this was really not right. So I adjusted it to 4-6%. Shut the car off, did a TPS Autoset, and walked away. Fast forward three weeks, and there's a break in the weather. I took the car and put some gas in it. No problem on startup. Get to the gas station, fill up, car falls flat on its face. Refuses to start. Get it running and it wants to stall when I go into gear and wants to continue to stall if I am not careful with how much gas is given. Finally got it going and got home. Car is warm (roughly 190°F to 200°F) so I check the IAC again. It reads ~25%. But I didn't touch the car for 3 weeks. Only change was the temperature outside. Adjust back to 4-6%, TPS Autoset, walk away. Fast forward five weeks, take the car out. Stalls when I give a little gas and let off. Same issue of not starting. Get it going, drive some more, get home. Check the IAC Position, reads 17-18%. Same thing. Didn't touch the car for five weeks. Only thing that changed was the weather.

    Help:
    I'm honestly really confused at the point. My IAC Position is changing, but I don't know how. I think it's the weather, but I'm unsure. What could be the cause, and how can I fix it?

  2. #2
    Join Date
    May 2014
    Location
    Bostwick, GA
    Posts
    368

    Default

    Post the tune file.
    Run a System Log.
    Run a datalog, and capture the issue.
    Post up.

  3. #3
    Join Date
    Dec 2009
    Location
    Connecticut
    Posts
    28,539

    Default

    This is a copy & paste from one of my other posts.
    Originally Posted by Danny Cabral
    For further assistance, post your Global File and a short datalog of this occurrence for us to analyze.
    Also, review the datalog and inform us of exactly where in the datalog (time/seconds) the problem occurs.
    Datalog & Global Files must be linked to a document hosting website. I use Dropbox.com.
    Files can also be "zipped" (compressed zipped folder) & attached directly to a forum post ("Go Advanced" & "Attachments").
    Your Global File is in the "Documents", "Holley", "HEFI V5", "Global Files" folder (.hefi file).
    Your Datalogs are in the "Documents", "Holley", "HEFI V5", "Datalogs" folder (.V5.dl file).
    Someone will analyze/troubleshoot the problem & offer advice. Also, ensure all this is right:
    http://forums.holley.com/showthread....ents-Read-This (Initial Checks & Adjustments - Read Steps #1-#6!)
    Overlay the datalog onto your Global File, and pay special attention to the center paragraph in blue print:
    Originally Posted by Danny Cabral
    Quick Datalogger Information:
    Always provide data, not just symptoms. Is the AFR & ignition timing optimized? Overlay the datalog onto your Global File.
    Ensure the Target A/F Ratio table is properly programmed for your engine. Ensure the ECU is "Learning" (Learn Table LINK).
    Scroll through the datalog to the problem area. Then look exactly where this happens on the Base Fuel & Timing Tables. Scrutinize:
    RPM, MAP, MAT, TPS, CTS, IAC, Target AFR, AFR Left, CL Comp, Ignition Timing, Duty Cycle, Fuel Flow, Fuel Pressure & Battery. When the engine is tuned & running well, you should decrease the Closed Loop & Learned Compensation Limits % to lock in a good tune.

    Using the Holley EFI software (LINK), look at where the live cursor moves to during this occurrence, and
    manually tune that area of the Base Fuel Table (enrich or lean) & Base Timing Table (optimize ignition timing).


    I find the most helpful datalog function, is overlaying the datalog on your Global File.
    I'm in the habit of using the datalog Overlay feature every time I review a datalog.
    Click on "Datalog" (on the top Toolbar), "Activate Overlay", then "Open Data Log".
    You can literally "playback" a recorded event, and watch it as it happened on any screen.
    Minimize (shrink) the datalog window, and move it to the bottom of any Global File screen.
    Then click & scroll anywhere on the datalog, and watch it playback on your Global File (EFI software).
    http://documents.holley.com/techlibr...9r10543rev.pdf (Holley EFI Datalogger Instructions)
    https://forums.holley.com/showthread...s-amp-Datalogs (Datalog & System Log Information - Read "NOTES")
    https://www.youtube.com/watch?v=iqHO...C6FEA0BB99AF17 (How To Record & Email A Datalog)
    https://www.youtube.com/watch?v=q7OZUXLRS1Q (How To Record A System Log & Diagnose A No-Start Condition)
    https://forums.holley.com/showthread...7531#post77531 (Closed Loop Datalog Tuning - Posts #2, #4 & #6)
    May God's grace bless you in the Lord Jesus Christ.
    '92 Ford Mustang GT: 385" SBF, Dart SHP 8.2 block, TFS T/W 11R 205 heads, 232°-244° duration/.623" lift/114° LSA camshaft, 12:1 C/R, TFS R-Series FTI ported intake, BBK 80mm T/B, Dominator MPFI & DIS, 36-1 crank trigger/1x cam sync, 200A 3G alternator, Optima Red battery, R134a 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, -6AN fuel system plumbing, Walbro 255 LPH pump, S&W subframe connectors, LenTech Strip Terminator wide-ratio AOD/3000 RPM converter, B&M Hammer shifter, FPP aluminum driveshaft, FPP 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 M/T Street Comp tires.

  4. #4
    Join Date
    Apr 2016
    Location
    Indianapolis, IN
    Posts
    5

    Default

    Here are some datalogs along with the tune. I was unable to get the car to stall out (I'm not sure why), but I was able to get it to pull the RPM down. Normally it'll start to do this, then continue down into a stall. Hopefully this is enough for someone to see what's happening.
    Attached Files Attached Files

  5. #5
    Join Date
    Apr 2016
    Location
    Indianapolis, IN
    Posts
    5

    Default

    After talking with a tuning buddy of mine, he suggested that the IAC could be changing due to heat expansion. Any thoughts to this?

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