High Engine Idle Speed After Coming off Cruising Speed

[RSS]

I have a 1994 Carver 350 Aft Cabin with twin Crusader 454XL Series engines with an idle issue I am trying to track down. Elevated idle speed (anywhere from 1000-1600 rpms) seems to only happen after cruising at 3,000 rpms or higher. I can run all day at less than 3,000 rpms and elevated engine idle speed problem doesn't pop up. Restart corrects the problem. Checked linkage, secondary barrels, and choke. Choke wide open. Not linkage issue and secondary barrels aren't sticking open. Also, I lubed everything up good. Last season starboard engine acted up and this year it is the port engine acting up. Seems to be an electrical problem because a restart always corrects the problem so far. If I adjust the idle speed stop screw while engine is idling high and lower the idle speed that way then after a restart engine won't idle because idle is set too low. Idle problem doesn't happen every time, but frequency seems to be increasing. Does anybody have any ideas or have you had same problem? Thanks.

[bud37]

Welcome to the forum....not sure if a 94 has this but if it does...have a look in your distributors and check to see if advance mechanism is free and not sticking, may be sticking with a bit a advance timing causing elevated idle...its a start and free.....good luck...

[tomschauer]

from your description, it sounds like these are carbureted motors. As such, they should have no electrical or electronic interface other than maybe a fast idle solenoid? If they have a fast idle solenoid, it should be a small cigarette lighter shaped cylinder next to the carb linkage with a single wire connected. Try disconnecting the wire. Other than linkage or worn butterfly bushings, I don't know what else it could be????

[hausherrs]

Mine was doing this. I have 454xli. I would bring it down to zero throttle and it would still idle at 1000-1200. So I would have to lift to about 25% and slam it to zero. Then it would idle at 800. And I could shut the engines off and restart and the high idle would be gone as well.

To fix it I just adjusted my throttle cable so that its got a little extra at zero throttle.

I know it sounds strange. I think theres some gunk in there and I bought some rebuild kits so the cable adjustment was supposed to be temporary.

But give it a shot and while you are down there check to make sure the butterflies move freely.

[Viper]

I've mostly ran into a sticking distributor advance mechanism or a sloppy/stretched cable. Depending on it's condition, you may be able to clean it up and free the advance mechanism. If the springs are rusted, they should be replaced. If it's a sloppy cable, replace it, no matter what you do it'll never be consistent for long.

[RSS]

Thanks for the advice everyone. Took a closer look this weekend and inside of distributor below rotor is definitely rusty. My Crusader 454XL engines have GM HEI distributors with knock sensors. If these distributors have a mechanical advance I think that is what is causing my occasional high idle.

[Viper]

Did you ever solve the problem or did she get hauled out before you could?

[RSS]

I can't say I got to the bottom of the issue. I was able to determined that my distributors don't have a mechanical advance. Therefore, I think the issue is an electronic problem of some type. One of the electronic modules must be advancing the timing or something like that. Prior to haul out, if problem surfaced I was always able to correct it with a re-start. I'm kinda at a loss right now until I can experiment with it a little more next season.

[Viper]

Check your cable, it's probably got too much play and should be replaced. You can try adjusting to take up slack but the issue will probably resurface eventually. next time it happens, leave it running at high idle and disconnect the cable at the carb. If rpm drops, the cable is your problem.

[RSS]

I was able to rule out the cable the last time it idled high. Disconnected the cable and no change in rpm speed. So far, a restart corrects the problem every time. I take engine out of gear, shut it down, restart it, and engine idles at normal idle speed. Has me scratching my head.