1998 Volvo Penta 5.7GSi High Idling Issue

DrBabyfood

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Aug 19, 2016
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Hey guys,

So I've got a 1998 Volvo Penta 5.7GSi that started idling around the 1800 rpm range. Background info: the boat was a gift from my father in law and he's always taken very good care of his toys. I took the boat out with my pops and it ran perfectly. We got to one area and noticed it seemed to be running a little rich however it didn't give us any problems and ran fine the rest of the day on the water. The next day, I hooked the water up to it to flush it out and upon cranking it I noticed the idle immediately started to increase up to around 1800 rpm.

I've checked the throttle cable and the physical mechanics of the throttle body and cleaned the throttle body as well. I noticed the IAC sensor wasn't connected nor was the knock sensor. I reconnected these and it didn't change the high idle. I've taken it to a mechanic to run diagnostics on it and he told me it wasn't throwing any error codes. He replaced the IAC sensor thinking it was that and the motor started to hunt from 600-800 rpm. The mechanic thought he noticed an air leak around the throttle body gasket so he replaced those and it actually changed the idle back to the initial high idle problem. He then said he checked the IAC valve and it was in the correct position so he thinks the ECM is working because it's trying to slow down the idle. Next up his plan is to check on the timing of the motor. He is admittedly stumped as well as myself.

Anybody have any ideas what the problem could be?
 

alldodge

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Howdy

Did the mechanic say anything about the throttle position sensor being in the correct position according to the scanner?
 

DrBabyfood

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I didn't specifically ask about it however he said the scanner was completely normal. I can try to follow up on this as well as the timing. All and any help is much appreciated!
 

alldodge

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Vacuum leak would cause some issues.

Why was the IAC and knock found disconnected? Was some other work done prior?
 

DrBabyfood

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The boat did have work done previously. I know the risers have been replaced as it has always been in salt water. My father in law took good care of the boat in terms of paying the mechanic at the dry dock he kept it at to maintenance it every year and etc. When I found the disconnected sensors he actually didn't even know about them. I find it very weird that everything was seemingly working fine without them connected.
 

alldodge

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I'm not a VP guy just trying to help until one of those guys come around. Not all but many times when the IAC is unplugged the idle will increase because some require a voltage to close the valve, otherwise its all open. If this is the case for your motor then I would suggest checking to see what voltages your getting on the pins.

SInce its GM it should work similar to Merc so here is how to test the Merc. a. Ignition OFF for 10 seconds.
b. Disconnect IAC harness connector.
c. Restart engine.
d. Using a test light connected to ground, probe each one
of the four IAC harness terminals.
Does The Test Light Blink On All Four Terminals?

Volvo Penta wiring diagram.jpg
 

DrBabyfood

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So an update (and even worse news) the mechanic looked at the timing and initially said it showed base timing and the motor was hunting between 800-1200 rpm. He replaced something in the distributor cap and rechecked the timing and it was working correctly. However, the motor then started to have a high pitched knock that he's never heard before. He's now telling me that it's probably something internal and I'll most likely have to replace the motor. I don't quite understand how the thing can go from working perfectly fine to idling high to then needing an engine replacement? Something doesn't quite make sense here. Or am I just in denial?
 

alldodge

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Sounds to me that you need to find a real mechanic, this guy is guessing. I'm pretty sure you have the GM EST distributer so the only thing to replace would be the module. Don't know why he would replace it, the motor was running. Just throwing parts at it. Your motor is a GSI (what are the rest or the letters)?

This is the worst part about having a VP, they are great motors, but when something happens to them there are few that know how to fix them. Same here on the forum, there are few here that know the motors. Wish I could be of more help, but find manuals for the motor is ruff.
 

DrBabyfood

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It's a Volvo Penta OMC GSi 57FCPBY engine. And yes I believe it was the module he was talking about replacing. It just doesn't make sense that the thing was running perfectly fine and then starts to idle high and then spirals downward to now it's knocking and having to be completely replaced/rebuilt. I do plan on taking it to another mechanic for a second opinion however I have to find one first. The mechanic that has it now is apparently a certified VP mechanic and says he went to mechanic school and etc.
 

GeorgeDes

Petty Officer 2nd Class
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Sep 30, 2013
Messages
107
Some similar idle issues including IAC and associated wiring and pins on my 5.7 GSI. Now looks like a burnt valve and no compression on one cylinder also a major contributor. Did the shop do a compression check on yours?
 

alldodge

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Think I would personally check the oil level and run the motor to listen for the noise. If you can record and post it might give us a hint.
 

DrBabyfood

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No they did not run a compression test on it. I should be going to pick it up tomorrow. I won't be able to mess with it for several days.
 

DrBabyfood

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UPDATE:

So I went to pick up the boat today. The mechanic didn't charge me at all. He said when he cold cranked the motor the knocking sound sounded like a piston slap or ring clip.
 

muc

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I'm not a VP guy just trying to help until one of those guys come around. Not all but many times when the IAC is unplugged the idle will increase because some require a voltage to close the valve, otherwise its all open. If this is the case for your motor then I would suggest checking to see what voltages your getting on the pins.

SInce its GM it should work similar to Merc so here is how to test the Merc. a. Ignition OFF for 10 seconds.
b. Disconnect IAC harness connector.
c. Restart engine.
d. Using a test light connected to ground, probe each one
of the four IAC harness terminals.
Does The Test Light Blink On All Four Terminals?


If you do this test.
I might be a good idea to make sure the test light meets the EFI requirements. According to the service manual, it must have a certain amount of resistance or it can blow out your ECM. I can't remember the exact amount but I do know that the test light (with a regular filament light bulb in it) I owned when EFI first came out didn't pass the test and I had to buy a new one that did. ---- just a heads up.
 

alldodge

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According to the service manual, it must have a certain amount of resistance or it can blow out your ECM.

Sure glad your helping out the VP guys, most time there is little input. With you here I'll try to stay out the way.

Also Merc manual only says
Using a test light with 100 mA or less rating may show a faint glow when test actually states no light.

Doesn't say anything about blowing the ECM
 

muc

"Retired" Association of Marine Technicians...
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Sure glad your helping out the VP guys, most time there is little input. With you here I'll try to stay out the way.

Also Merc manual only says


Doesn't say anything about blowing the ECM

Happy to help when I can but please don't "get out of the way" you give a lot of very useful advice and I pretty much only come on here when I'm stuck somewhere with my iPad and an Internet connection. You on the other hand are a lot like Don S (man I still miss him, we fought like 2 young kids when we both started posting here and I think it made us both better people --- well me anyway, I think he was always a good person) so I'm sometimes a little reluctant to post because I'm not sure when I'll be back. But you are helping all the time. So if some of my posts seem like I'm slamming you or somebody else, I apologize because that's not what I'm trying to do. I'm just trying to add info that might have been missed. Or because some of the posters don't know how big of a difference there can be between engines and manufactures. So please don't get out of the way.

Now onto the test light thing. It was in the manual but I'm not sure if it's in the current manuals. And that's one of the problems with factory manuals. They are written for a trained technician so they assume that the reader has been to their school and has read all of their previous manuals. And that's why I add things to other people's posts. But don't hesitate to call me out when you think I'm wrong. I'm a opinionated SOB who thinks he's always right. But I'm human so I'm quite often wrong.

DrBabyfood, sorry to hijack your post. You asked if the sequence of events are normal. Yes and no. Sometimes one problem leads to another and sometimes it's just bad luck. Mechanics can be wrong (we are human) or they can be incompatant usually, somewhere in between. If you want to learn how to fix your boat yourself there are a lot of people here that will try to help. Or try a different mechanic, while there are a lot of bad mechanics out there. The are some good ones. The good ones just want you to be honest with them and of coarse pay us for our time. I sounds like the one you had look at it might have been over his head (didn't charge you) or didn't want to start guessing. I'm reminded of one of the places I worked at. The service manager is looking at 3 of us and says "I've got 3 MerCruiser master technicians standing here telling me they're not sure what's wrong with this boat" and we replied as one "yup, sometimes we got to guess when we don't got all the proper test equipment"
So you might want to call your mechanic back now that he's had sometime to think about your problem and see if anything new has popped into his head. Sounds to me like he's an honest one.
 

StingrayMike

Petty Officer 1st Class
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Aug 17, 2014
Messages
355
Might be alittle late, or not even relavent at this point.....
but was the motor "aactually idling high" or just indicate on the gage?

I have 5.0 GXI ( Still trying to figure out the ins and outs) and she says she is running high by the tach, but not really.
my issue, I believe, is just a dirty sensor.
might be too late, but if the motor is not shot, something to consider.
 
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