Paging Redlowrey

[ECU1984]

I have a lot of respect for your Suzuki troubleshooting skills.
Could you please look at my2004 Df140 IAC trouble thread and give your opinion?
Thanks
Motor cranks instantly, smooth idle and runs out good to 5800rpm,
Will run perfectly for any distance, then as you slow down back to idle and shift into neutral, it knocks off .....will instantly crank right up and run good all over again
Everything I read points to IAC valve, throttle plate is clean, new plugs, new filters, VST is spotless, etc. CTP continuity test was perfect also.
Noticed it idles at 800 rpm and that's high according to specs
Bought new IAC valve and followed instructions to calibrate/adjust it to the 650 rpm idle
turn the adjustment screw under rubber plug on throttle body until tach goes over 1000 and I get the beeps and the duty cycle thing is in effect,
I set the idle to 650 rpms while still beeping, bump throttle up to take it off duty cycle and the procedure goes just as the directions describe.
Then motor instantly goes right back to 800 rpms, the IAC adjustment wont take effect.
Have you seen this before? I don't believe i bought two bad IAC valves, I read a post where someone described the exact same issue and said they finally changed the ECU and it fixed it.
Thoughts?
Thanks

[redlowrey]

First thing to do is check when the closed throttle switch actually signals on, run the engine on the muffs and set up your multimeter on volts and slide a thin needle down the side of the connector, connect up your meter leave the switch connected and start the motor up.

The computer sends five volts down the single wire and when the contacts close the voltage will drop to zero, ideally you want this to happen just before you hit neutral.

So start the motor shift into gear bring the rpm up to 1500 and watch the meter, slowly bring the throttle back and see when the five volts drops to zero, as I said just before neutral.

I want you to check the coolant temp sensor voltage also, if the signal voltage is to high, it might be the reason it is idling a bit higher, at operating temp it should be under One volt.

If the voltage is sitting between one and a half and Two volts pull the thermostat out when the engine is cold and see if it stays open.

[redlowrey]

I should have added if you are inexperienced remove the prop, if you know what you are doing, be careful.

[Moonlighter]

Red - do you have any thoughts on this thread? Bit of an out of the ordinary thing being asked.
https://www.suzukioutboardforum.com/...nator-question

cheers!

[ECU1984]

Thank you Sir!
I hope to find time to test both tomorrow afternoon, Will let you know the results

[ECU1984]

Results :
1) Checked the temp sensor that screws into the head while running and warmed up and it read .98V
2) Closed throttle switch read 0.01V with engine on and in neutral at idle, as soon as it engages into gear it jumps to 13.78V and stays there as throttle increases.
I took it up to 1500 rpm in gear and kept it there for a minute or so and I slowly brought it back to neutral and it stayed 13.78 - 13.79 the entire time and as soon as it hits idle
it instantly goes to 0.01V. It felt to me like it was switching where and when it should. It closed to 0.01V right when the throttle hits idle (800rpm) and just a micro tad before dead neutral.
There is 0.01V when closed and 13.78V when open......nothing in between those two voltages. Never saw a 5V reading or anything close to 5V
Thoughts?

[redlowrey]

Ok temp sensor is fine providing it is the same at pin 9 on the ecu, closed throttle switch is working fine, I thought zero five for your engine, but that is for 60, and 70 hp, your engine zero 12 or battery voltage.
As I said I like to see the change in voltage just as you are going into neutral.
The switch is working, the thing to check, is the computer delaying the timing and changing the duty cycle on the iac valve when the closed throttle switch goes to zero. Have you got a timing light and a good meter with duty cycle so when the closed throttle switch goes to zero you can check and see what happens. It would be good to know what the duty cycle is at idle, something is telling the computer to idle at a higher rpm, check the voltage on the IAT sensor

All engines with a throttle body and plate will have a small amount of air bypassing the plate while the engine is running, this is set at the factory, the main idle adjustment will be done by adjusting the air bypass screw while the iac valve is set at 15% for your engine, this means at 650, 700 rpm the iac valve has plenty of margin to keep the idle stable for in gear and trolling conditions, for some reason your engine is shifting to 800rpm as soon as you come off idle mode.

I thought it may have been still in warm up mode with high temp voltage,

[ECU1984]

IAT sensor: Intake Air Temperatrure?
Is that the sensor that is plugged into my plastic air box in front of the throttle body?
If so, what should the voltage be? running or not running w/ key on?
Thank you, I really appreciate the help!

[redlowrey]

Yes, depending on air temp, unless you have snow on the ground I would think below 3 volts, have you got a timing light and a good meter with duty cycle. Is the engine stalling before you hit neutral or in neutral, does it stall every time you shift into neutral, it is important that you can check the timing and duty cycle when the switch closes, and when you open the throttle, and also to see if it advances when you put it in gear and open the throttle.

Do you know how to check the operation of your map sensor, very important sensor

[ECU1984]

I have a Snap-On timing light, my Dad was a Nascar engine builder. I inherited all his tools. I grew up in an "old school" muscle car garage. I am 61 and know my way around
a combustion engine (understand fuel, spark compression and timing). Lost on electronic controlled systems w/ numerous sensors and ecu. Though, I am enjoying learning and
doing my own work, The internet really cuts the learning curve and folks like you sharing your knowledge.
So, I have a timing light but not a multimeter, just a plain volt/ohm meter i use for voltage readings, resistance readings and checking continuity. I will buy a digital multi-meter as I also want to learn more on how to test stators, etc and think I need to learn about peak voltage capturing.
I just found the instructions for testing the IAT sensor and the MAP sensor, will do that tomorrow but I do have an update
I may have found the issue, maybe not:
I sat the cowl down on my garage floor and noticed a few tiny sticks and some leaves that were under it when I picked it up and they weren't there previously.
Upon further inspection, the air vents in the rear of the cowl have a sort of duct work channel for air path up to the front air box. Well, out of sight and around a bend in the duct channel was a clog
of leaves/twigs like bird nest and also a mud dobber had caked up the nest, I had to take the cowl pieces apart to clean it all out. Maybe poor air flow? It was completely packed. The front air box had leaves in it as well
Hope to run it this week on the water and see

[redlowrey]

That could do it, if it was running a bit richer, when you pull the throttle back from wide open to closed throttle, being rich could make it stall if it was rich, this was something I was thinking about when I said check the temp sensor voltage being high it would run a bit richer and would make the engine idle higher, I think you would have noticed the porcelain inside the plugs would have been black indicating it was running rich. If you are going to buy a meter bite the bullet and spend a bit of money on a good graphing meter.

For me there is never a day that I have not got my oscilloscope hooked up to something, if you know how an ignition system with a distributor works, you will have no trouble learning how electronic systems work, I know lots of mechanics that would not know how an old points and condenser dizzy with mechanical and vacuum advance works.

[ECU1984]

I know lots of mechanics that would not know how an old points and condenser dizzy with mechanical and vacuum advance works.

That made me smile

[ECU1984]

Finally got to run the boat today for the first time since finding the "bird nest"
Ran like a scalded dog for an hour, varied speeds, WOT, trolling and idleing, couldn't get it to stall
and hit the highest mph I have seen on it. Fingers crossed and thinking the air restriction was the issue