Inconsistent-variable idle on a 225hp OX66

I have read thru quite a few posts now on potential idling problems on the OX66 engines, but my problem is a little different. I have twin 1999 225hp OX66 engines (S/L 225TXRX's). The port engine runs great. The starboard engine runs great at high RPM's, but at low RPMs (800-1300) it shakes quite a bit more than the port, and at idle (neutral) I am getting variable readings of RPM. Sometimes this engine will idle high (10-1100 RPM), and other times it will idle low (500-600 RPM). The idle speed, whether in neutral or in gear, will change almost every time I turn the key switch on/off. Sometimes, if the engine warms up, the RPM's will drop back to normal range, and stay there throughout the day. Other times, they will vary -- tending to run higher
(900-1100). I have adjusted the idle set screw many times, and this does not seem to make a difference. Sometimes I can't even adjust the setting low enough to drop the RPM's into normal range. I can set the screw, and have to adjust it 15 minutes later. I brought the boat to a 5 star Yamaha shop recently, and they adjusted the TPS sensor and made a few minor cable adjustments, but the problem still exists (better, but still not right). No codes were obvious on the flash reader. One other problem that is troubling me is that on this same engine, I am getting a 2-3 second "dieseling" run-on effect after shutting the engine off. Not every time, but probably 5 times out of 10, it will run for an additional 2-3 seconds after turning off the key switch. The port engine does not have ANY of these problems. Any ideas/feedback would be greatly appreciated! I am not sure what is going on at this point, and am not sure if the problems are related in any way or not. Since most of these parts (O2 sensor, ignition switches, TPS sensor) are expensive, I would like to have a bit more direction before I start replacing parts to troubleshoot. Also, just as an FYI, the engines both reach 5400-5500 RPM WOT, and push the boat in the mid 50's top end speed. No problems with horsepower or compression. All cylinders compress between 115-120. I don't have any service history on the boat. Bought it used just a few months ago. The idle and run-on issue on the starboard engine has me concerned, and I'm having trouble isolating the problem. Thanks in advance for any suggestions you may have!

Re: Inconsistent-variable idle on a 225hp OX66

I'll take a stab at it before Rodbolt responds...

I think you have a couple issues.
1) for the run-on condition, could be your key switch is defective? does pulling the safety lanyard switch kill the motor immediately?

2) the rpm at idle issue could be related to a stuck/faulty thermostat. An open tstat would cause the engine to not get up to proper operating temps causing the ECU to adjust fuel for a cold motor. timing would be fixed to 7BTDC and code 33 would be present.

Also, those motors shake a lot. The idle screw really doesn't do much on those motors. proper idle is achieved by setting the TPS correctly. linkage disconnected, and TPS voltage set to .60-.62v.

Re: Inconsistent-variable idle on a 225hp OX66

Thanks. I will try the kill switch and report on that issue.
Regarding the TPS...my service tech said that it was set at 0.72, and he adjusted it to 0.50+/-.002?? That's what it says on my receipt.
That does appear to have settled some of the shaking, but yesterday I had the boat out and noticed that it shakes excessively between 600 and 1100RPM, in gear. Above that it does better. I also do notice that my fuel management gauge shows that the right engine burns more fuel than the left across all RPMs (approx 20-30% more)...is this normal?
I'll get back to you on the kill switch later today.

Re: Inconsistent-variable idle on a 225hp OX66

Pulled the kill switch and the motor shuts off immediately. Able to duplicate several times. I'm assuming this means that the problem is either with the ignition switch or wiring harness?? Also, as far as the thermostats go, I don't know if this helps, but when the engines first start up, they run at higher RPM (1200-1400) but after a minute or so they drop down a few hundred RPM. Where the starboard engine lands is still unpredictable.

Re: Inconsistent-variable idle on a 225hp OX66

clean and test your O2 sensor. One of mine was faulty and caused a higher fuel consumption condition.

www.boatsetup.com/O2sensor.pdf
disregard the bench/flame test.

Re: Inconsistent-variable idle on a 225hp OX66

cousinabe said:

Also, those motors shake a lot. The idle screw really doesn't do much on those motors. proper idle is achieved by setting the TPS correctly. linkage disconnected, and TPS voltage set to .60-.62v.

Click to expand...

My bad, should be .50-.52. Your settings are spot on.

Re: Inconsistent-variable idle on a 225hp OX66

Thanks Abe!
I'll check that O2 sensor, and get back with you. Would that cause all/most of the symptoms that I have outlined in this post?
Thanks for your help.

Re: Inconsistent-variable idle on a 225hp OX66

Ill watch and observe.
dont think an O2 sensor is your issue but this should be fun .

Re: Inconsistent-variable idle on a 225hp OX66

Cleaned the O2 sensor per previous posts, but did not check with a volt meter yet to confirm normal operation. Really did not seem that dirty. A little carbon build up, but the hole in the tube was clear and all in all, looked pretty clean. My bet is that this part was serviced within the past year. Checked the plugs, and all 6 look good. Checked the throttle linkage again, just to be sure that it stopped in the middle of the arrow. I did have to adjust again (since having it serviced). Made sure all the backing nuts were tight, and it did seem to make the idle speed more consistent -- at least on the hose. Weather permitting, I'll be out on the water tomorrow, and will check out the overall performance.
I'd be real curious as to what you are thinking, RodBolt.?
Someone suggested that I try swapping parts from the good engine (port) to the starboard until I find the culprit...I hesitate doing this as I don't want to end up with 2 problems instead of the one. The left engine seems to be running great, and I really don't want to mess with it. Let me know your thoughts on that.
BTW, when warm, and when operating "normally", both engines tend to bottom out at 500 RPM (per gauges) in forward gear/idle. I am assuming that I should increase this to 625-650? This is going to increase my idle at start up a bit, but after it warms up, this is the correct RPM setting, right? I know the specs are between 700-730, but it really doesn't specify in gear or neutral idle. 700-730 in gear is going to put my neutral idle around 900-1000 RPM, minimum.
Thanks again. I look forward to your response(s).

Re: Inconsistent-variable idle on a 225hp OX66

PS, any thoughts on the "shaking"? The two biggest issues here are the inconsistent idle, and the low speed shaking, particularly when compared to the port engine. Port engine barely shakes at all, no matter what speed, load, or RPM. Starboard is still finicky.

Re: Inconsistent-variable idle on a 225hp OX66

if you're getting node codes:
check your fuel pumps. when were these last changed.
Perform a link and synch.
also, check that your spark plug caps are in spec 4k-6k ohms.
When was your VST last serviced along with the fuel pressure screen cleaning?
Are you using a good battery with clean connections?
I am assuming your spark plugs and prop are in good shape.

Rod, unfortunately, I went back to the working world this week and have not had much time on here ... Don't let the guy wait too long if I'm leading him in circles!!

Re: Inconsistent-variable idle on a 225hp OX66

cousin, your doing well so far.
list all the issues that can cause the ECU to drop CCS and fix timing at 7* BTDC and remember one that fixs timing at 7* BTDC will allow timing to advance just not retard below 7* BTDC hence the fast idle.
cleaning the O2 sensors without checking the output voltage is like taking a shower with your raincoat on .
remember, OX66, if the sender is unplugged no codes are set but the ECU sees the open circuit, fuel is fixed rich at low speed and lean above 4000, DO NOT run above 4000.
however if its a bad signal the ecu will detect it and react and can lean out the injector pulse width above 4000.

Re: Inconsistent-variable idle on a 225hp OX66

I knew it was that damn thermo sensor! Make sure it's working, in spec and plugged in.

Re: Inconsistent-variable idle on a 225hp OX66

I saw a good post that might help with your engine not shutting down clean issue.
http://forums.iboats.com/showthread.php?t=288319

Re: Inconsistent-variable idle on a 225hp OX66

I'll check out the thermo sensor, and reviewed the link on the run on condition. Will let you know what I find, but it makes sense. Ran the boat both Sat and Sunday, and it is pretty close to dialed in...Stbd engine takes a few minutes longer than the port side to drop to normal idle rpm (still stays around 1000-1100 until it is run for about 3-5 minutes). Seems to be falling into a more consistent RPM range at idle after it is warmed up...still have a slight shake between 800-1200 in gear. Overall, TPS and throttle linkage adjustments have improved the condition...both engines seem more in sync, but the stbd still needs a few tweaks. Thanks again for the feedback.