400i starts fine runs smooth then rough.

Discussion in '365 GT4 2+2/400/412' started by Anthony bentley, Sep 3, 2021.

  1. Anthony bentley

    Anthony bentley Formula Junior

    May 20, 2006
    Full Name:
    Anthony Bentley
    My car is a single distributor S2 that starts fine and runs smooth but after a few minutes idles rough and cuts out when selecting drive, I can’t work out if the cold start is staying on, none of the plugs are fouled, I’m thinking of buying the gauges to balance it, out of interest where do you attach the balancing gauges on the injection if I attempt this myself?
    Also when in neutral what should an auto car idle at?
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  3. Ewan

    Ewan Karting

    Jul 5, 2015
    Dorset, UK
    Mine did a similar thing. Rebuilding the distributor and fitting new injectors was the cure for me, and it’s now running like a dream. Whether this is what’s wrong with yours I don’t know, but may be worth checking.

    GT4SBLUE Rookie

    Jan 4, 2017
    Full Name:
    Hello Anthony I have a 79 400I auto which I have had a deal of time on to make it run nice.
    You need a manual to follow the steps to tune the engine and another manual to set up or at least check the vacuum operating the autobox.
    the systems are not so bad to work on but you need to do it twice.
    the idle speed is 1000 to 1100 but I found I had a thump as the auto selected and it was pulling the car at idle.
    I have the ignition retarded to 5deg at idle to allow for not running on 100+ octane and the idle speed at 900rpm cold which drops to around 600rpm when not cold thats above 35deg. the idle is smooth and the drive selection cannot be felt.
    if the plugs look very good check that both banks are the same and that one or both are not weak.
    idle and running is greatly improved with the correct and balanced co figures.
    v power petrol I find a must.
    you have lots to do.

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