Iac

[RichRab]

2002 merc 5.0 mpi alpha 1 gen 2.Can someone tell me what an iac valve is and what it does? When I took the boat out of the water last season it kept stalling. A couple of years ago we took a ride in the ocean and every time we stopped the motor stalled. I took it to the dealer and the iac was replaced. Now it seems like at idle the motor is loading up with fuel. If I put it in neutral and rev up to around 1200 rpm it is smooth. I put it in gear and it stalls. Any way to check or bypass it? There is not any beeping or alarms sounding. Thank you. RR

 

[dubs283]

Re: Iac

IAC = idle air control valve

it controls the amount of air entering the intake at idle, simple

they are a common replace item on mpi mercs, issues with them can be accompanied with an alarm and a fault code, but not always. to properly diagnose an iac you need a cds and must know the default values on the data items list to troubleshoot properly

 

[RichRab]

Re: Iac

I was doing some research and another site said to use an ohmmeter. I have 2 wires and it reads about 10. It said ford has two wires and gm has four and gm reading should be over 200. Thank you. RR

 

[dubs283]

Re: Iac

mercruiser hasn't used a ford engine in over 30 years, testing with an ohmeter will only give you a static reading

to properly see usable values the engine needs to run with a cds connected so you can see the duty cycle of the iac

 

[scoflaw]

Re: Iac

Did you change the IAC filter as well? Located in the TB

 

[RichRab]

Re: Iac

It was replaced last year. Thanks

 

[CaptainMak]

Re: Iac

So the engine won't stay idling at 650-700rpm unless you give it some throttle ? How long will it idle before shutting off this way ?
How long ago was the IAC valve replaced by the dealer ? I just had one go out after about 10 hrs on the water.

BTW, your throttle position sensor might be something to look at also. Not sure if the MPI's have them, my EFI does and they go bad too.

 

[dubs283]

Re: Iac

BTW, your throttle position sensor might be something to look at also.

right, and the only way to "look" at the throttle position sensor is with a scan tool, otherwise you're just guessing as to what the problem is

to op:

you need to buy or borrow a scan tool or take the boat to a place that can look at the data itmes/fault codes for you

 

[CaptainMak]

Re: Iac

right, and the only way to "look" at the throttle position sensor is with a scan tool, otherwise you're just guessing as to what the problem is

ummm, no..... to test the TPS you need to get an OHM meter and test resistance at different throttle levels. 0%, 25%, 50%, 100% and that should give you pretty good indication if it's shot or not... so ya....

 

[dubs283]

Re: Iac

ummm, no..... to test the TPS you need to get an OHM meter and test resistance at different throttle levels. 0%, 25%, 50%, 100% and that should give you pretty good indication if it's shot or not... so ya....

yes that is one way to test the tps, but i have seen tps that ohm tests fine but when put into the system and lake testing the scan tool tells a different story

 

[achris]

Re: Iac

I was doing some research and another site said to use an ohmmeter. I have 2 wires and it reads about 10. It said ford has two wires and gm has four and gm reading should be over 200. Thank you. RR

My IAC shorted and burned out a few months ago. The new one has a value of 10.1 Ohms (read on the Diacom software)...

mercruiser hasn't used a ford engine in over 30 years, testing with an ohmeter will only give you a static reading

to properly see usable values the engine needs to run with a cds connected so you can see the duty cycle of the iac

Correct about using a Ford engine, but the IACs Merc are using are from a modern Ford V6 engine....

So the engine won't stay idling at 650-700rpm unless you give it some throttle ? How long will it idle before shutting off this way ?
How long ago was the IAC valve replaced by the dealer ? I just had one go out after about 10 hrs on the water.

BTW, your throttle position sensor might be something to look at also. Not sure if the MPI's have them, my EFI does and they go bad too.

Yes, MPIs have them...

yes that is one way to test the tps, but i have seen tps that ohm tests fine but when put into the system and lake testing the scan tool tells a different story

Agreed...

OP, you really need the software to have a look at what the ECU is doing. If the value of the IAC is 10 you can 90% assume it's electrically good. One of the other problems with IACs is they sometimes seize , so remove the IAC from the engine and check the spindle is free to move. If it isn't you might get away with spraying some carb cleaner in there and freeing it up....

Chris....

 

[RichRab]

Re: Iac

I was just thinking that a mechanic did work on boat last year and told me the iac was on the way out. No idea how he concluded that but I was unhappy about some things so I will not be calling him. Also I have a post about the drain under the starboard manifold under heading of risers that maybe someone will have some ideas on. Thank you, RR

 

[achris]

Re: Iac

... Also I have a post about the drain under the starboard manifold under heading of risers that maybe someone will have some ideas on. Thank you, RR

Already answered that one...

 

[CaptainMak]

Re: Iac

If you want to risk about $25, go to NAPA and get part # 3-1755 for the IAC. This is the 4 wire one though. I think you might have a 2 wire that might be different. I just replaced mine. Took the boat out this weekend for first run of season. Flawless !

 

[RichRab]

Re: Iac

Two wire.

 

[CaptainMak]

Re: Iac

Two wire.

NAPA AUTO PARTS

About $48.

 

[achris]

Re: Iac

2002, it more likely to be this one....

http://www.summitracing.com/parts/smp-ac423

 

[RichRab]

Re: Iac

I was talking to an auto mechanic who said to look for a constant reading on the tps with ohm meter. Also to take the vacuum hose off the fuel pressure regulator if equipped and make sure no gas is getting through causing a rich condition. Thanks.

 

[RichRab]

Re: Iac

I checked the tps with an ohm meter and the ohms do not change as the throttle is opened. Unsure if it is supposed to change. I was told it should without fluctuation. Unsure which is correct. I replaced the iac and it still is not right. Idle around 600 and as the speed is increased the motor bogs down and around 1000 rpm it sounds fine. If I put it in gear it sputters and stalls. When I took spark arrestor off there is an elbow for the PVC hose is going into intake manifold that fits very loosely that I thought was a vacuum leak so I put a clamp on but it did not help. I restricted air into throttle body and that does not help so I don't think it is a vacuum leak. No fuel in pressure regulator vacuum side. Thank you. RR

 

[Fun Times]

Re: Iac

I checked the tps with an ohm meter and the ohms do not change as the throttle is opened. Unsure if it is supposed to change. I was told it should without fluctuation. Unsure which is correct.

Yes if you tested the TPS correctly compared to the service manual, the readings are supposed to change without fluctuations.

There is also a voltages test that could be done that should read between half to five volts as the TPS moves.

Have you found your service manual online yet? Most are available online if you do a search.

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