2004 horizon 6.2 mcm mx mpi with IAC wide open vaccum leak

[stang32]

i tuned up this boat last week and this week it would not start without giving it full throttle. once started, there is a large vaccum leak which i narrowed down to the IAC assy. i pinched one of the hoses coming from it and the air leak diminished so i figured it was a bad iac motor, i replaced it only to have the same issue. i do not have a scanner(yet) so i do not know if the IAC is getting signal to operate. so what can cause the IAC to stay open?
when the key is on and i remove the IAC connector, the alarm sounds, once quickly so i believe the computor is monitoring the IAC correctly.

 

[alldodge]

tuned up this boat last week and this week it would not start without giving it full throttle

You have something disconnected that was not before. The vacuum line connects to the fuel pressure regulator. Do you have an Alpha or Bravo drive?

 

[stang32]

i thought about that but there was nothing touched, the plugs, cap, rotor and wires had nothing in the way that needed to be disconnected, the boat ran fine after the tune up, and 2 days later when i put as new belt on it, the boat then sat for a few days and then would not start without increased throttle . the boat will idle but the air leak is rediculously promenant and as i said ,when i pinch one of the hoses coming from the IAC, the air leak goes away and the idle becomes more stable. it has a bravo drive

 

[alldodge]

Pinch the hose and it runs better so there is the leak, now to determine if its the IAC, the hose or a connection.

 

[stang32]

check out this photo . hoses 19 & 20 are connected to the IAC base and one goes to the intake manifold the other goes tothe throttle body. both hoses are connected properly, the IAC is the only thing that regulates the controlled vaccum (air) leak. now, the iac is staying open, causing this massive leak. i need to find out why the iac is not closing and regulating the air flow

 

[stang32]

the IAC is new and acting the same as rthe old one

 

[alldodge]

Agree, but what you have is either a IAC which is not working correctly (new bad one) or a defect somewhere. I don't see it being the lines, so this leaves either the electrical connection to the IAC, the sealing surface or something is wrong with the new one.

That said this is without having any info of scanning the motor. If motor was scanned it should have codes

 

[stang32]

yes, i agree, a scanner would be a big help and i am buying one but this is whats in front of me right now. i do not believe the new iac is faulty. what i need to determine is what input sensor directs the iac to open/close. i know obviously that the computer ultimately controlls the iac but the computer needs input to direct it. as i learned years ago, garbage in, garbage out. if the information the computer is receiving is incorrect, then the commands will be incorrect.. i will be back at the boat tomorrow to plug in a noid tester to the AIC plug and see if i get power on that circuit

 

[alldodge]

All sensors are feed by 5V, would use a voltmeter

 

[stang32]

yes but correct me if im wrong doesn't the IAC run off of 12V?

 

[alldodge]

yes but correct me if im wrong doesn't the IAC run off of 12V?

No 5V note letter I

 

[stang32]

i see the diagram but the pink wire goes to the fuse holder, A. also the same wire feeds the fuel pump relay. all signs point to it being 12V. ill find out tomorrow when i test it with a voltmeter

 

[Fun Times]

The loud air sound you hear may just be the IAC muffler missing that should be item number 6 in your diagram though it is missing from view when clicked on....See item # 6 here inside the throttle body housing, http://www.mercruiserparts.com/bam/s...31956/11652/80

Being the pink wire is running to splice 106 indicates it's a 12v system...Any of the gray wire system would make it run on the 5 volt system. That mentioned the IAC uses the 5 volt ground side for it's grounding system that should be a Black/Pink wire being splice 100.

Splice Number: Description:
106 Switched 12 Volt Fused
101 5 Volt Transducer Power
100 5 Volt Transducer Ground

The idle air control (IAC) valve is a 12 volt circuit powered by the MPR. It is located at the top rear of the engine. A malfunction of the IAC will set a fault of IAC Output.

 

[alldodge]

My bad you and FT are correct

 

[stang32]

well , fun times, you were right on the muffler, shure enough, it was missing, i installed a new one and it was nice and quiet, once that was resolved, i took it out for a ride and intermittently at high throttle points, i would hear a knock, kind of thought something was banging aroung in the cubby or engine bay but no, its coming fro mthe engine, and when it happens, the engine does not hiccup, stumble, or show any signs that something is wrong, rpms stay steady.
i am taking it out for another ride tomorrow with someone else at the wheel so i can investigate while driving