Idle and above idle throttle question

[purplehayes]

Hello All...

First off thanks to everyone for the info on my last post which resulted in me changing the IAC on my port engine.

I have a 2002 Amberjack 290, with twin 350 MPI shaft drive engines. My question today is this:

The port engine is the worst but to some extent the starboard engine is similar... I can idle the engines (troll or slow through marina waters) in which case the engines sit at about 630rpm... If I am gentle on the throttles I can increase the rpm to about 850rpm but then it hits a definite change and the engine jumps to like 1200-1500 rpm, nothing in between.

I assume the initial engine control is with the IAC and not the main throttle body but my question is should I not be able to increase the RPM slowly up through the lower 1000's, why the jump.

I tested it today after changing the IAC on the starboard engine (had two suspect idle loss of power situations) and at the dock with no load on the engine it jumped from 850rpm right up to 1500rpm and it was virtually impossible for me to get anything in between.

Thoughts please.

Additional and likely important info: The throttle and gear controls are separate on my engines. Two knobs for the gear and two for throttle.

Cheers

 

[Dave S]

I don't know whether it might affect your RPM problem, but did you change the IAC filter as well on your port engine? You can read my post on the problems I had with my IAC and you will see the role the filter plays as well. http://clubsearay.com/forum/showthread.php?t=27561&highlight=controller

 

[purplehayes]

I don't know whether it might affect your RPM problem, but did you change the IAC filter as well on your port engine? You can read my post on the problems I had with my IAC and you will see the role the filter plays as well. http://clubsearay.com/forum/showthread.php?t=27561&highlight=controller

Hi Dave,

The link is taking me to a page which says that I dont have enough privileges to view it.... do you mean the IAC muffler or the lower section which connects to the two hoses?

I did not replace the lower section and the muffler was not in place on the port engine and the starboard engine muffler was very dirty so I removed it. I am still waiting for those parts to come in for me to install.

Cheers

 

[Dave S]

I am not sure why you can't see the post but it sounds like the muffler won't be the problem since it is not in place.

I really don't have any idea why the RPM jumps up like that. But since the IAC was the only thing you changed, I would be suspicious of it first. Could you swap the two IACs from port to starboard to see if the problem moves with the swap? At least that will confirm whether the new IAC is any way to blame for the issue you are having.

Dave

 

[purplehayes]

I am not sure why you can't see the post but it sounds like the muffler won't be the problem since it is not in place.

I really don't have any idea why the RPM jumps up like that. But since the IAC was the only thing you changed, I would be suspicious of it first. Could you swap the two IACs from port to starboard to see if the problem moves with the swap? At least that will confirm whether the new IAC is any way to blame for the issue you are having.

Dave

Hi Dave,

Thanks for your interest... I dont think that the IAC is the issue as the engine was doing this before I changed the IAC's on both engines.

Cheers