Rip

Nevermind, fondulac doesn't have a new IAC, so I cleaned the old one and stuck it back in again. Hopefully compressed air and wd40, does the trick

baja bailey

Rip

What kind of problem are you having? Last year my 502 would start and idle fine for the first start of the day, but after it warmed up and you turnded it off, it would not start without help and then would not idle at all. My mechanic said the IAC checked good but took it out to look at it anyway and the plunger on the end was broken off. Put in new IAC and no problems since. Strange things happen....

Rip

Thanks kindly for the input

Here's what happened, I suspected problems with the IAC since I had the fuel injectors serviced and cleaned, and reinstalled them myself... things were better, but the engine still idled rough and the longer it idled the worse it got, yet once the throttle was opened up, and the butterflies allowed enough air to pass through and clear the buildup of fuel it ran smoother and smoother...

so I talked to a dealer on Saturday. No IAC's available.

I took the old one out, and noticed it was dirty,

sprayed the s..t out of it with wd 40 and air

took the boat out today...
at first I had the same roughness, but after I ran it a bit longer, things improved

I went to my Monday to Friday parts supplier expecting that I would need to back order the IAC, I wanted one anyway and would wait

He had it in stock , so I rushed back to the boat, and re and re'd the part.

I haven't had it out yet, but I did notice that the old IAC which I had cleaned, had a very shiny input/output shaft. This was very rust coloured before and after I cleaned the old IAC, so maybe after the WD-40 it just needed a few actuations to unstick itself a bit and clean the crud from the shaft.

So maybe this will help a few people, by suggesting before and after layup to clean and lube the IAC with air and penetrating oil so it doesn't get sticky?

blackhawk

Okay, this may be off topic a little but definitely related. I told a mercruiser mechanic that I adjusted the idle on my motor(1995 502 EFI) with the set screw that actually moves one of the butterflies.

He told me to NEVER do that because it can screw computer settings up. So, I asked him what it was there for? To which he just looked at me and said "I have no idea".

So, what is it there for and is it safe to use it?

paradigm shift

Well I can not take credit for it but I cut a pasted this info from a post on this board. Good information. It is long.
_____________________________________________

How to adjust IAC & TPS" On Merc EFI

If your engine surges, does not immediately follow the throttle movement, dies when put in gear or runs up when taken out of gear- then you probably have either a TPS or IAC sensor to be tested & or adjusted.
First- the equipment needed:
1/2" wrench or socket to remove the throttle body
7/16 wrench to disconnect the throttle cable
5/16 wrench to loosen & tighten throttle cable adjuster
1/8" ball end allen wrench
Digital dc voltmeter or Mercruiser scan tool (best & easiest)
Timing light.

1st-Warm the engine to operating temp, then set the base timing as required for your engine configuration
(Procharged set at 10* base in base timing mode (scan tool)
Do not take a timing reading off the scan tool at idle, it
varies radically. Use only the timing light.

2. Disconnect the throttle cable from the throttle body.
3. Remove the throttle body from the intake...... carefully unplug both cable plugs from the unit. Now you have good control over it, turn it over and find the two set screws that adjust the Primary (left) & the Secondary (right) throttle blades. Of course the Primary opens first but with EFI, the idle is NOT adjusted on the Primary side. Remove part of the loc-tite holding the screws in place.
To explain: The IAC sensor measures the amount of air supplied thru the IAC Tube between the throttle blades. This is a fixed size and can only flow so much air. The IAC is adjusted with the screw under the secondary blade of the throttle body. Therefore, it is a "relationship" adjustment!! The more air that flows through the Secondary throttle plates is aire that does NOT have to be supplied by the IAC (Idle Air Control motor) The IAC actually pushes a valve in and out in reaction to the air tube flow.

TPS- identify the TPS mounted under the throttle body but over the Primary throttle blade shaft. There is an adjustment screw ajacent to the sensor.
4. Plug the cable leads into the TPS sensor. Plug in the scan tool to the ECM. Turn the ignition ON, but do not try to start the engine. Set the scan tool to TPS voltage (or connect DVM) then set the adjustment screw for the lowest value & still touching the throttle arm stop. This may be .045-.065 volts.

5. Reinstall the throttle body, but do not hook up the throttle cable as yet. Don't forget to plug the control leads into it.

6. Restart the engine. Rewarm the motor.
7. On the scan tool select -IAC voltage
Now before we adjust the IAC we are going to test the IAC control. Slowly put your finger over the IAC tube and partially block it. The engine should start to stumble, lose rpm or die. This is good & means the IAC control is good. Now to adjust it.
NOTE: I used a flexible 1/4 socket drive shaft to snake under
the intake with a torx wrench in it to reach the allen
screw adjustment as it is not reachable behind my
intercooler with a plain allen wrench.
Insert your allen wrench or ajustment tool into the 1/8" screw. Turning the screw in (clockwise)will reduce the IAC voltage reading (it opens the secondary throttle blade). Turning it counter-clockwise closes the blade causing MORE air to come thru the IAC tube & increasing the voltage. DID YOU NOTICE THE IDLE SPEED NEVER CHANGED??? The total air flow at idle remains constant, it is the SOURCE of the air flow that is important to the ECM & sensors. I recommend you verify the required setting thru a Mercruiser Manual or you engine builder, or ECM Programmer. Arizona Speed has recommended to me to set to .035v. It works. Not to disparage knowledgable Merc mechanics, but most "professed" Merc mechanics in smaller shops have no idea what the values should be. Ask to see the book.

8. Final & last step- recheck your base timing. You might actually be surprized... it can change on you.
Another NOTE: The spark timing shown on the scan tool at 2000 rpm can vary by a wide margin because of the Merc timing tables by 400 rpm either side of the 2000 figure. This reading is not absolute- do not trust it. Use only the timing light to calibrate timing!!

This was a hard fought learning process for me. I hope it helps you all. I am beginning to figure out that EFI is about relationships, not necessarily direct readings or adjustments. Adjust one thing to make something else change......
it can make you...

Strip Poker 388

iTrader: (6)

It changes the amount of air at idle ,and changed the tps also, it does change the computer calibrations . there it something called a count its suppose to be set at around 30-40 . you set the idle with a merc ddt tool .i just bought one and trying to learn all the stuff. On one of my 500 efi,s it turns over more than normal when trying to start. the idle doesn't stable for the frist few seconds.
See if the tech has a Manuel you can read up on .or a DDT

blackhawk

Wow, great info! I need to invest in a DDT scan tool. I would like my boat to idle as low as possible. With the blackhawk drive it moves pretty good at idle which sucks in no wake zones!

How much is a DDT tool? I assume they are pretty expensive. I thought I was told you could buy an adapter to use a GM auto scan tool? I have a couple friends with them.

Strip Poker 388

iTrader: (6)

The DDT and harness and module for merc i paid around 1100.00

blackhawk

Thanks for the link formula! After reading paradigm's post(several times) it appears that what I actually did was adjust the IAC. .

The reason I did it was I was out one day and out of the blue my boat would stall every time I put it in gear. I got home and put it on the muffs and started looking for something that had come unhooked and found nothing. I then noticed the set screw that actually moved the secondary butterfly. Grabbed an allen wrench and turned it a couple times and bumped the idle up about 250 and no stalling. I am not familiar with EFI systems(obviously) so I figured it was some type of idle adjustment until a mechanic told me not to mess with it.

Looks like I just got lucky!

bichaum

Hi I was just wondering if anybody can help me. I have a 30 campion chase with a 500hp in it. The motor barely idles more often stalls at start up and even when warm. You can not pull all the way back on the throttle when coming to a stop because the motor will ramp down and most of the time stall. I've done everything from a complete tune up to a new IAC motor. I've watched the plunger move when the motor come to a stall, but when idling it does not move when cold. I am lost, any ides. The computer was shipped out and came back all ok als. the boat runs strong when running but just doesn't want to idle.

Thanks