Tech Help Needed: 02 Four Stroke 225 Rough Idle

[final cut]

the motor runs well in all phases of operation except when throttling back to neutral. when placed in gear the motor wants to stall at low rpm.no buzzers or alarms just extremly rough idle . the problem dissappears when i shut down and restart the motor. i have trolled at low speed for hours taking the motor in and out of gear without having this occur but as soon as i increase my speed 4000rpms to move to another area and back down to neutral the problem returns. i have checked for fuel problems,and using ring free additive ,checked fuel filters, plug wires all ok . All shift and throttle are ok. Could it be a shifter switch or thermal sensors or is something else going on? Motors have approximately 450 hrs. Appreciate all help.

 

[bossee]

Re: Tech Help Needed: 02 Four Stroke 225 Rough Idle

Hi,

Do a search on:

rough idle

in this forum and I'm sure you will find some suggestion what to try. Remember to see in post if it is 4-stroke and EFI since Your outboard has both. Probably someone with Yamaha F200 or F225 had this problem before and posted it here and hopefully some suggestion how to solve it. It may take a while for you to browse through all "hits" you get when searching on rough idle but be patient and you will probably find something.

I may mention that I have a Yamaha F115 4-stroke EFI myself and I had problem with rough idle and it died after some time at idle. After some search under the cowl I found the cause - it was the fuel filter that was not mounted correctly by the Yamaha dealer at last service. When I mounted it back correctly it did not leak anymore and have run fine since this.

/Bo

 

[rodbolt]

Re: Tech Help Needed: 02 Four Stroke 225 Rough Idle

your F225 symptoms are classic for a defective or sticking idle control motor, some manuals call it an ISC and some an IAC. what it does is control the air at idle speed.
it sounds like its either failing to close correctly.
you can bypass it and manually throttle the air. the air inlet for idle speed is the gray hose from the ISC on the port head to the rear plastic cover. you can also manually activate the ISC with the laptop to see if its working as the engine will react to a change in the ISC setting.
at 4000 RPM the IAC is set to 100 percent, if at idle it cannot reset to about 67 percent it does not idle correctly usually with a laptop it will show higher than normal intake pressure. in extreme cases it will acually set a manifold pressure sensor failure code even though its the ISC that failed. it happens.
the ISC can become mechanically stuck and the ECU cannot detect it. all the ECU sees is that electrically the ISC is connected.