Idle speed to high Merc 230E 1996. Engine idling speed goes itself up
to about 1.6 revs and never comes down. At start-up it stays just
below 900 revs until I press accelerator to increase revs and after
that it only goes down to about 1.6 revs and stay high. I consulted
the garage ( Merc specialists but not Main Dealer ) they diagnosed the
engine with their computer and advised me to change Mass Air Sensor
( which according to the computer was faulty ) I  changed the Mass Air
Sensor, but this did not help at all. Now the garage says "change the
Throttle Body". I took off the throttle body cleaned it ant took the
plastic cover off to check the mechanism inside. Mechanically
everything there looks OK. The motor moves the butterfly valve when
accelerated and comes back to it's lowest possible position. I am not
experienced mechanic but my logic conclusion is that this device is
working OK ( at least mechanically ).  I checked for vacuum leaks, but
everything looks OK. As an experiment, I took off the whole air
conduct from the throttle body and left air inlet totally opened. The
idle speed was exactly the same ( high ) as with all attachments
fitted. I wonder if there is anybody on the forum who came across
similar problem and may have some solution.
Please help. Thank you for any suggestions. Mark, London