Adjust S38 Throttle Bodies

To complete the reassembly of the throttle bodies, they needed to be mechanically adjusted to BMW specifications. I purchased an electronic digital  indicator, which measured in millimeters and inches. Per the BMW technical procedure, I pre-loaded the indicator to 2mm at the edge of the lowest point of the throttle butterfly. I loosened the locknut and closed the butterfly completely. This of course moved the indicator, so for my purpose, I reset the pre-load to 2mm with the butterfly completely closed. I then adjusted the stop screw for each butterfly between 2.10 and 2.15 mm, trying to be closer to 2.10. Tightening the locknut usually increased the opening, so it took a few attempts to get them to be locked close to 2.10 mm.

I then replaced the three push rods and now understood why the fixed push rod on the 5/6 throttle body was set to 97.5mm while the other two push rods were set longer to 100mm. This part of the procedure uses the dial indicator to shorten the 1/2 and 3/4 push rods just to the point that the dial indicator moves, which then ensures that all of the pushrods are equal length. I then measured all of the throttle butterfly openings at wide open throttle and adjusted the six throttle stop screws to get the average top and bottom openings as close to spec as possible.

Now I was ready to finally hook up all of the remaining vacuum lines and hoses, install new o-rings on the intake runners, and reassemble the intake runners to the plenum using the boots. The assembled intake was then installed and secured to the throttle bodies.

The last step before firing up the freshly tuned and adjusted S38 was to change the oil. I had poured some fresh oil over the cams and valves before I secured the valve cover. After draining the used oil, I decided to fill and drain the engine one more time in an abundance of caution because the valve cover and intake had been off the car for so long. I didn’t actually start the car, but cranked it over for a while with the ignition unplugged just to get the oil pressure up. I then drained the clean oil and then filled it again.

The oil filter housing had always been half-covered in cosmoline. I now used my ultrasonic cleaner to get it all cleaned up before inserting a new oil filter and installing it on the car.

2 Replies to “Adjust S38 Throttle Bodies”

  1. Hello,

    This manual is amazing, but iam stupid enough to not understand from where you measure 2mm ?
    I replaced one butterfly clap and i have to adjust it, but i don’t understand how do i measure it ?
    How did you pre-load it. At first i tought you making gap between clap and throttle body right.

    Maybe you can tell me in simple words how do i measure it with digital/analogue indicator, from what i measure ?

    Kindly thank you and wish all the best !

    Warm Regards,

    Kindly thank you and

    1. To paraphrase something I found on the web, “To get accurate measurements, your dial/digital indicator should be “pre-loaded”. By this we mean that the pressure of the contact point (probe) on the work piece being checked should be set to 2mm.”

      When setting up the indicator, basically have it measure 2mm to start with the probe at the edge of the throttle body flap.

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