Posted by daveyk [173.245.54.13] on Friday, February 12, 2016 at 20:33:26 :
In Reply to: Re: 1988 W250 High idle at start up posted by Steven [162.158.255.90] on Friday, February 12, 2016 at 19:52:05 :
Steven
O2 - oxygen sensor / sensors in the exhaust used to control fuel system for rich or lean conditions. usually operate from zero to 1 volt and should switch hi / lo of .5 volts.
AIS = Automatic Idle Speed or idle air control. used to control idle speed.
If on start up the AIR pump is pushing air into the exhaust manifold and blowing over the O2 sensor the computer thinks it is a lean condition, richen up the fuel mixture, and raise the idle speed.
HTH
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