Re: Mercruiser tbi idle around 1800
one of the largest culprits of the 1800 rpm idle is a bad IAC motor. they can test good with the laptop or the scan tool but be mechanically bad. while its running at 1800 do you hear a very loud whistling sound from the TBI assy? but there are a few other causes. but the engine has to have increased air to make rpm as well as fuel. if the tps is set to high the timing will increase, the injector pulse width wil increase and the IAC will go to near 100 % cause the stupid puter cant tell its out of adjustment of defective. it just sees a signal that the throttles were opened.. but usually if while its running you take your finger and manually block off the IAC air passage and can control the RPM it will be in the IAC circuits.the two normal modes to hear the IAC scream are its running out of fuel or its stuck in the open position.
sorry no manual just a basic wiring diagram.