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Thread: Cobalt SS/TC - Rough startup Idle after stock replacement PCM? What to HP tune?

  1. #1
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    Cobalt SS/TC - Rough startup Idle after stock replacement PCM? What to HP tune?

    Any HP tuners on here? My car came with a locked Trifecta tuned PCM. I just recently swapped in a stock replacement PCM. After installing the stock PCM, my car has a very rough idle when you first start it when it’s cold. Almost like it’s cammed. After the 1st initial warm up it’s perfectly fine and idles smooth. I didn’t have this with the Trifecta tuned PCM. Being that PCM is locked, I am unable to pull the information from it to see what they had the settings for it. So I am wondering what should I try adjusting in the PCM to help with the cold startup? I have already HP tuned the car and its running great besides the start up idle.

    09 Cobalt SS/TC
    HP Tuned @21psi
    K&N SRI Intake
    Hahn Upper IC pipe and Intercooler
    Cat & Muffler Delete

    Also should I just stick with 21 PSI or push it any farther? My car does not have the 3 bar sensor upgrade.
    2000 Buick Regal GSE Ported Gen III SC with 3.0” Pulley, Northstar TB, ZZP Ported LIM, ZZP Stage III IC, Comp VS Cam, Comp 105 Springs, Viton Valve Seals, 42.5 Injectors, PRJ Gen II Fuel Rails and Racetronix Fuel Pump with HD Harness, TOG Headers with 3” Catted Downpipe, ZZP 3” Dual Stainless Cat-back, Dynotech Stage II Trans, 3.29 Final Drive, 2750 stall converter, GTP Engine Cradle Mounts, Front Motor Mounts Spun 90*, JMB 4” FWI, Autolite 104’s, 180* stat, GMPP Handing Kit, Moog Endlinks.

  2. #2
    Senior Tuner cobaltssoverbooster's Avatar
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    There are no warm up table adjustments it's one of the many shortcomings of the unlocked portion of the lnf ecu. I'm working on some ideas now that I'm witnessing snow season in reno but I haven't reviewed enough data to figure anything out.

    In the meantime most people set cams to full park at idle and turn the cat warm-up cycle off.

  3. #3
    Senior Tuner cobaltssoverbooster's Avatar
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    Factory sensor limit is 23 psi. You can run that but start lower and tune your way up so you don't exceed the sensor cap. Factory turbo is good for 24 psi tops and no more. We already exceed maximum shaft speed at 24 psi and anything over generates extra unwanted heat.

  4. #4
    This is of course true, but I've peronally always had great luck with a combination of cam timing and a slightly raised idle speeds in cold temp areas (1200rpm or so). I've personally never once had cold start issues with any of the LNF's I have tuned, even in subzero temps with running e85 as well.

    OP, try the tune file I sent you the other day and report back for whether or not it helped your issue at all.

  5. #5
    Potential Tuner
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    Not an advanced idea but just checking an obvious,

    Is the old tune "startup" idle rpm the same as the new one?