If your tech thinks it's too hard to get too, He better find a new line of work!! I just checked and adjusted the low idle on our 300sdl today and it took all of about 3 minutes.

On the rear of the fuel injection pump is a round cover called an actuator. It is about 2 1/2 " in diameter, its plastic and at the top is a two wire plug in. This is how you adjust it according to the factory manual.

Engine at idle, unplug the connector from the acuator. The rpm should drop slightly, (My engine was so far out of adjustment it almost died) check the idle rpm it should be 570 =/-40 with the engine @ operating temp. If it needs an adjustment, the jamb nut and screw are about 1" to the front of the connector you unplugged for the actuator. the jamb nut is about 13mm, and the adjustment screw is a bout a 5 or 6mm, real small. Back the screw out to increase the idle. once you get done with that tighten the nut and plug the actuator back in and the idle should " briefly increase". If you don't notice an increase the actuator might be burned out.

After the screw is set you can tweak the idle using the trimming plug. A round dial located by the fuse box. It's about the size of a quarter with numbers 1-7. Lift and turn to adjust. But do the other adjustment first. Then try this.

Good Luck

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87' 300sdl