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
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 ?
There is a vacuum line in the back of the engine behind the throttle cable
There is a vacuum line at the transmission on the driver side to the
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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