high idle

[redlinemc]

Hey Folks!
I got a 150 v6 mercury outboard and all of a sudden the rpm’s at idle won’t come down to where it’s supposed to be….
Anybody dealt with this?
Got a few things to check I know but if anyone can please advise before I go ahead and check vacuum lines or throttle plate sync that would be amazing!

 

[Chris1956]

Some of those motors have a thermo valve, which allows extra air to raise revs. You might see if it is working. Trace some vacuum lines to the head.

 

[Dukedog]

what year? efi or carb?..

 

[Dave1027]

Is the timing control arm against the stop? It should be when at idle. That's the first thing to check.

 

[redlinemc]

what year? efi or carb?..

89 carbed

 

[redlinemc]

Is the timing control arm against the stop? It should be when at idle. That's the first thing to check.

Some of those motors have a thermo valve, which allows extra air to raise revs. You might see if it is working. Trace some vacuum lines to the head.

Think the primer bulb line if bad would allow to much air?

 

[Dave1027]

Think the primer bulb line if bad would allow to much air?

That would not cause a high idle. A problem with the primer bulb would cause a loss of fuel to the motor causing it to quit running.

 

[redlinemc]

That would not cause a high idle. A problem with the primer bulb would cause a loss of fuel to the motor causing it to quit running.

Ok thx Dave!

 

[redlinemc]

Is the timing control arm against the stop? It should be when at idle. That's the first thing to check.

K ya I’ll check that, jus a side note that it ran at proper rpm’s for 20 seconds or so then rpm’s went up and every start after that it was high rpm’s

 

[Chris1956]

If the thermo valve is not closing after warm up, or the vacuum hose to it is leaking, the idle RPM would be high.

 

[redlinemc]

If the thermo valve is not closing after warm up, or the vacuum hose to it is leaking, the idle RPM would be high.

Hey thx Chris! I’ll check it out!

 

[redlinemc]

If the thermo valve is not closing after warm up, or the vacuum hose to it is leaking, the idle RPM would be high.

If the thermo valve is not closing after warm up, or the vacuum hose to it is leaking, the idle RPM would be high.

Chris what about the idle lever being stuck on at the throttle lever even tho it’s in the down position. it used to b a little stiff but now moves real easy

 

[Chris1956]

Gee, not sure what you mean by idle lever being stuck.... Cold start lever on control?

 

[redlinemc]

Gee, not sure what you mean by idle lever being stuck.... Cold start lever on control?

Yes the fast idle on control

 

[redlinemc]

Yes the fast idle on control

Guess I should’ve said the mechanism on the inside of control box not returning to normal

 

[Chris1956]

Well, the cold start lever should be able to stay down. It could be an issue in the control, like dirt, or the control cables could be misadjusted. With the cold start up, the control will not usually allow the throttle to be pushed forward.

Disconnect the throttle cable at the engine and see if it works right. If not, you will need to disassemble and clean the controller.

 

[redlinemc]

Well, the cold start lever should be able to stay down. It could be an issue in the control, like dirt, or the control cables could be misadjusted. With the cold start up, the control will not usually allow the throttle to be pushed forward.

Disconnect the throttle cable at the engine and see if it works right. If not, you will need to disassemble and clean the controller.

U mean the cold start (fast idle lever) could b stuck in fast position in the inside of controller or can I tell by looking at the engine cable side ? I would I know by just looking at it?

 

[Chris1956]

Not sure what you are asking. The cold start lever should move down and stay there, if working properly. If not, there is some sort of issue with controller or motor adjustment.

 

[redlinemc]

Not sure what you are asking. The cold start lever should move down and stay there, if working properly. If not, there is some sort of issue with controller or motor adjustment.

Fast idle lever stuck hence the high idle in neutral that won’t come down

 

[jimmbo]

Did it work fine before? If so, did you do anything to the Control Cables, like anchoring/securing them?