Idle speed to high Merc 230E

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
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You definitely got a vacuum leak. Use carburator cleaner and spray at suspected leaks to see where it affects the engine.
Maybe some of your vacuum line cracked and leaked.
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Hi, Thank you very much for your suggestion. I thought the same, but could not find any vacuum leak. The conduct from the air filter to the Throttle Body looks OK. The rubber pipe which goes to the engine top cover is also looking OK. Do you know any other places where to look ? How to check the leak with carburettor cleaner ? Thanks again, Mark. Another thought. The engine idle speed in these cars is electronically controlled isn't it ? Do you know if this can be adjusted or tuned up by special equipment ?
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There is a vacuum line in the back of the engine behind the throttle cable assembly.
There is a vacuum line at the transmission on the driver side to the modulator.
There is also a yellow checkvalve by the firewall...
There is the brake booster line... that may develop crack.
No idle speed adjustment whatsoever.
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