Question for Steve Brotherton

[endeavor]

I have a 89 300TE. Idle speed decreases by 150rpm going
from Park to Drive. Never used to do that before. Almost has been doing for a year or so.
I do have the Bosch electronic part that goes inside the air mass flow which I have been told gets dirty and stuck but replacing it is quite tricky.
My warm idle speed in drive is about 550 while in park it is around 700 rpm. The car does not die except the engine shakes as the idle speed is so low.
Can you tell me where this diagnostic to increase the idle speed by disconnecting something at the ECU, can you please send me detail instructions, also, replacing injectors, would that help the idle speed??
Please let me know any MB gurus??
Barry