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Thread: NA 1UZFE vvti (GS400) rough Idle

  1. #1

    Default NA 1UZFE vvti (GS400) rough Idle

    Hello all.

    Newbie MAPECU3 user here requesting some insight from you guys.

    Testing out the water so to speak and want to get to learn the MAP3 so I am on an NA set up (for now) OEM injectors, No boost just bolt ons (headers, intake, exhaust).
    Wired the MAPECU3 in MAF intercept configuration using a jumper harness.

    Lexus GS400 1998-2000 MAPECU3 wiring diagram.pdf (Typo for "VG" pin. goes to pin #10, not #25. No pin #25 for E3 connector). Verified.

    No known problems with MAPCAL or the USB drivers.
    Using a TPS base map I found on here for a 1UZ.

    TPS inputs have been adjusted to match TPS meter on the dashboard.
    No connection errors.

    Turn the key Engine starts.
    However, it struggles to idle (cold start):
    Drops down to below 500RPM (almost stalls) them shoots back up to over 1000RPM. But it dosent shut off.
    After the engine warms up a bit the idle gets a little better but is still rough.

    Any reason why the idle is so rough?
    I am using a base table provided on the MAPECU forums for a NA configuration (TPS) for a GS400.

    I have not made any adjustments to the base table.

    Thanks in advance.
    Last edited by Tank; 14th-October-2018 at 05:16 AM.

  2. #2


    It's hard to say as the base table is configured to pass through the MAF and ignition signals. We might have to see a screen shot of the MAPCAL dashboard or log file to see what is going on. Essentially the MAF Input must match the Fuel Output on the dashboard. Also, it is vital that the cylinder firing order is as per the diagram and there is no ignition channels crossed over.
    MAP-ECU Support

  3. #3


    Ok as I discussed with Pete from sales I will double check the wiring, try again and get you a screen shot of the MAPCAL dashboard readout and record a log file.
    I’m hoping is a wiring issue cause Pete says there should be no issues with a base loaded map.
    Here is what he said just to keep us all on the same page:

    “It sounds like the OEM ECU is not seeing a valid MAF signal or ignition signals are not correct as it should run 100% normal with a zeroed out base table and correct wiring. Can you please send copies of the wiring diagram we provided, a copy of the base table and a log file would be an advantage?

    Just to check, I assume all your OEM ECU wire colour codes matched our diagram?



    I’ll see if I post a small video clip of the issue as well.
    Thanks for the reply.

  4. #4


    Ok, that would be great, thank you. It's probably easier if we help you on the forum now. A photo/video of your MAPCAL dashboard should help a lot.
    MAP-ECU Support

  5. #5


    Well Peter was right. It was a wiring issue. Went back and proceeded to check my wiring one by one and found that one of the ignition coil leads was not soldered all the way thru. Re connected the wire and car starts right up no problem.
    Thanks again for the support.

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