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spinxt

Idle RPM...

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spinxt

I pulled my 2000 RLX (320Hp Monsoon) out of storage last weekend, cleaned her all up, and last night I decied to fire her up for the first time. Since this is my first high-quality fuel injected ski boat, I was quite surpised when it fired up on the first turn of the key Thumbup.gif However, I think the idle RPM is too high. It's idling just above 2K RPM. I don't remember it idling that high last season. When I bliped the throttle and dropped down to just around 1K RPM (which seems more normal), but it gradually rose back up to 2K.

Any thoughts?

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jgouveia3

first thing i'd check is to make sure that the cable is not binding, and if you have PP, make sure that the "string" is tight.

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spinxt

No PP, and the cable is sliding smoothly. When I would blurp the throttle and pull it back, it would drop down right away. Plus when the throttle is in the natural position (12 o'clock), the butterfly valve is completely closed. The only air getting to the engine at that point is through a small hole in the part of the valve toward the stern. It couldn't close anymore than it already is.

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RTS
The only air getting to the engine at that point is through a small hole in the part of the valve toward the stern. It couldn't close anymore than it already is.

You will also get some air through the Idle air control valve on the fuel injected engine. This valve, controlled by the ECM, uses bypass air to control the RPM when, like you say, the butterfly valve is closed. It accounts for engine temp, altitude variances, etc. It goes out of play once you open the throttle and therefore open the butterfly valve.

My thoughts would be the Idle air Valve (doesn't Indmar call it the AIC?), first, then (but very unlikely) the ECM.

Edited by rts

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sauer

I had the same problem last season. It turns out it was a throttle position sensor. If your throttle acts normal when the motor is up to operating temp that probibly the culprit. You can check the ohms of the sensor to see if its funny. the meter should start out at a low number and slowly rise with the pull of the throttle, if there is a big jump in numbers or if at idle you have a large reading thats probibly the problem. My echelon was idleing at around 2 also, but would sometime search and rise and fall in rpm. I was told that the automotive counterpart would work if it was started in the 12:00 position, if you started it with a little throttle it would not know you have a closed position at startup and have no power. A shutdown period of 10 seconds is all it takes to reset the computer to return to normal settings. I went with the automotive version but remember that all marine products are more resistant to sparking. I bought the automotive one and sprayed it with undercoating to seal it. hopefully that works.

Edited by sauer

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maliboo
I pulled my 2000 RLX (320Hp Monsoon) out of storage last weekend, cleaned her all up, and last night I decied to fire her up for the first time. Since this is my first high-quality fuel injected ski boat, I was quite surpised when it fired up on the first turn of the key Thumbup.gif However, I think the idle RPM is too high. It's idling just above 2K RPM. I don't remember it idling that high last season. When I bliped the throttle and dropped down to just around 1K RPM (which seems more normal), but it gradually rose back up to 2K.

Any thoughts?

My guess would be The IAC (Idle Air Control). It is a little stepper motor on the back side of the throttle body. It opens and closes to let air bypass the throttle body and control idle speed. If you take the flame arrestor off you can see the opening (3/8") on the top back side of the throttle body. Spray a little carb cleaner in that hole and turn the key on and off several times to ungunk the threads of the IAC. You can even undo the fastners and pull it out of the throttle body to spray it down. Sometimes using the boat is all it takes.

If blipping the throttle returns it to normal it might be bad and will have to be tested and replaced by a Malibu mech.

Good Luck I hope this helps.

Dwayne

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spinxt

If it is the Idle Air Control, why would a Malibu tech have to replace it? It seems like a pretty simple thing? Is there more involved than the obvious (ECU flash, etc.).

Chris

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electricjohn

It has to be calibrated to its zero point or base point, just like your engine timing. With a little experimentation you could probaly figure it out. But before you get that involved, check for vacuum leaks on the intake manifold area, making sure everything is tight. For instance, a loose throttle body will cause idle to go high.

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spinxt

I don't know if this means anything or not, but while it's idling, it seems like it's sucking air through that little hole in the butterfly valve more than it did when it was idling at the correct speed. If I put my finger over that hole, it pretty much stalls the engine out. I just don't remember the sucking sound from air going through that hole as loud as it is now.

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Baddog
I don't know if this means anything or not, but while it's idling, it seems like it's sucking air through that little hole in the butterfly valve more than it did when it was idling at the correct speed. If I put my finger over that hole, it pretty much stalls the engine out. I just don't remember the sucking sound from air going through that hole as loud as it is now.

Don't mean to be mean but I am going to have to say: "Duh" on this one. The idle hole provides a path for air to get into your engine when the engine is idling. Cover the hole = no air = no running engine.

Engine idling at 1000 rpms will require X amount of air. Idling at 2000 rpms will require X*2 (or more) air. That's why you feel/hear more at the higher revs. Lower idle = less air moving = less air movment noise. This is purely a physical observation and likely not related to the cause of what is going wrong.

Good luck.

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electricjohn

The IAC is in a parrellel path to that hole. Its like a(second) adjustable hole.

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spinxt

Ya, I guess that wasn't very "Captain Obvious" of me Whistling.gif . I'm armed with a can of carb cleaner and I'm sure I'll get to the bottom of it this afternoon when I work on it.

Chris

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CedarLakeSkier

Rather than looking for a deep problem, I just thought I'd ask a question.

Did the engine get a chance to warm up? I couldn't tell from your description. I pretty sure that engines idle slightly higher until they get to operating temp. I think bumping the throttle like you did may override this "automatic" occurrence.

either way, I was trying to give you hope that there wasn't any problem... Biggrin.gif

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spinxt
Rather than looking for a deep problem, I just thought I'd ask a question.

Did the engine get a chance to warm up? I couldn't tell from your description. I pretty sure that engines idle slightly higher until they get to operating temp. I think bumping the throttle like you did may override this "automatic" occurrence.

either way, I was trying to give you hope that there wasn't any problem... Biggrin.gif

I did let it warm up, the operating temp was up to 160 F and the RPM was still up near 2K.

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seasun7

Our trouble is similar ! at least it share the pain.

I opened "idle not stable" in the forum.

My boat is doing that for 1 year and after half doozen of qualified guys with different diag computers .... still not working. Hope it won't do the same for you.

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Baddog

I had a bad engine temp sensor a couple of years ago and although the primary problem was very hard to start when warmed up, it also idled high (~1500-1800) because, although the engine was in fact up to temp. the sensor was telling the computer it was cold and therefore running in a rich mode. Changed the sensor, a $20 part and 10 minutes to change, and all has been perfect since then.

Give it a go.

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