mercruiser 350 mag fast ideling issues

I have a 2001 Falcon Striper Delux 23ft. boat, Mercruiser 350mag with bravo outdrive. Replaced the short block in 2006 from mercruy. The ORIGINAL engine serial number is omo70241, model no. 4442067N1, 300 H.P. 5.7 litre

When ideling at low speeds (1000 rpms) often the motor will rev up to a very fast idel, so fast I can't shift to neutrel. I kill the engine, restart, and it usually will begin to idel down. It may run fine several times, then the same thing will happen again. Sometimes it will also sputter and seem to miss at low rpms (doesn't happen often, though).

I have cleaned the breather and wiped out the throttle body, and that seemed to help for a few weeks. But now it is doing the same thing again.

Do you have any ideas that I might try before taking it in to a repair shop?

Re: mercruiser 350 mag fast ideling issues

First thing to check is to disconnect the throttle cable from the throttle body and see if it will slow down to it's proper 600 rpm. If it does, you need to adjust the cable properly with just a slight preload to the idle position.

Re: mercruiser 350 mag fast ideling issues

Don S said:

First thing to check is to disconnect the throttle cable from the throttle body and see if it will slow down to it's proper 600 rpm. If it does, you need to adjust the cable properly with just a slight preload to the idle position.

Click to expand...

I will try this, although I really don't think this is the issue: because this happens so intermittently. It will run fine, at normal rpms, then suddenly increase the rpms. This usually happens while moving slowly or in nuetral, not going over 1000 rpms when it happens. When I kill the motor then restart it, it always quits the fast idel and goes back to 600-800 rpms as it should. Thanks for the advice anyway- I am desperate, so I will try it.

G.A.

Re: mercruiser 350 mag fast ideling issues

When you disconnect the cable... I would check the throttle cable and make sure it moves freely. I had one that was sticky (corroded inside i assume) and caused all kinds of problems. Goodluck!