Iac on 7.4 mercruiser

zaverin1

well my buddy finally replaced the iac sensor on his 7.4
i thought he did earlier but I was mistaken 
he calls me and says that after putting the new iac in his boat now idles at 2000rpm
he did notice that new iac was extended and old one he took out had a retracted plunger. I told him that computer should control the plunger and it makes no difference once plugged in.

i just never heard of a high idle after iac replacement.
he put the old one back in and it’s back to normal besides now he needs to crack the throttle open to start like before
weird?

Liberty44140

When I replaced the iac on the 5.0 of my last boat the oem iac came with instructions to make the new iac learn the boat. A start/stop time deal. Did he do the learning process?

zaverin1

I don’t know

davidbrooks

I had a high idle after my engines got reinstalled.  Mechnanic came in looked at it for 5 min and said..."Bad IAC".  Bought one for $250 and installed it and still had high idle.  Kept looking and found a vacuum hose that had come loose and was close but not connected.  Reconnected it and the idle came down to 600 rpm.  

Look for loose or missing vacuum lines.

zaverin1

Ye I will tell him to look for a vacuum leak