Mercruiser 5.0 MPI idling problem

[ZafSC]

Popular idling problem. The flame arrestor is clean. Replaced the IAC valve but no change. Removed and put back the little sponge in the throttle, but no change other than the hissing noise that I don't care (The engine is loud enough). I measured the fuel pressure a while ago, no problem (forgot the reading but it was normal). Engine runs just fine while moving on the water.
When running on the muffs on the land, no problem at all. I let it run for 15 minutes, engine was warm and idled nicely. On the water, when cold, it always starts no problem. After the engine warms up, it is slightly harder to start, but starts anyway (eventually).
The biggest problem that really sucks is, just about when I am around the dock, with the other boats around, when I try to change gears (forward-reverse) that I need to do often for maneuvering, engine stalls and stops. If it didn't stop idling, it would mostly stop when I try to get into gear. That is a panic situation near the dock, because while I am struggling, the boat keeps drifting. (That is no problem in open water, because nobody around, and I can take my time).
I am thinking of increasing the idling speed. To the left of the flame arrestor on the engine, I see a long stick with some screw adjustment on it. I guess it is the throttle control. If I can increase the idling speed by changing the length of the stick, is it a long-term acceptable solution? Because I saw on this forum that idling speed is all automatic and under IAC control (which didn't help replacing).
I will try to post the pictures soon, if I can arrange my cloud server.
Thanks

 

[nola mike]

Does it only stall when you're going into/out of gear? Is this an alpha or bravo?

 

[ZafSC]

It is Alpha Gen2, Sterndrive. When on gear and moving, engine is just fine and smooth. When I put into neutral, it idles roughly, but sometimes keeps on and continues. If it happens to be smooth idling, than gear mostly works. But rough idling, it is sure to stop when moved into gear.

 

[ZafSC]

I put the relevant pictures below..
The throttle and flame arrestors are clean.
The idling stick and screws are shown. I plan to increase the speed if this group approves it.
Thanks in advance...

Idling problem - Google Drive

drive.google.com

 

[nola mike]

I put the relevant pictures below..
The throttle and flame arrestors are clean.
The idling stick and screws are shown. I plan to increase the speed if this group approves it.
Thanks in advance...

Idling problem - Google Drive

drive.google.com

Unapproved. That's your throttle cable adjustment, not made for adjusting idle. Almost sounds like your shift interrupt, but shouldn't cause it to idle rough. Tough to diagnose without a scan tool, but I'd check to make sure all cylinders are firing when it's idling rough.

 

[alldodge]

It does fine in-gear and rough in neutral
As nola mike mentioned it's the shift interrupter. The switch is staying engaged and causes the rough idle. Might need adjusted, lubricate linkage or replaced

 

[cyclops222]

3 possibilities.
Incorrect IDLE mixture screw setting for a warmed up engine
Idle speed is too low when engine is warmed up.
Intake vacuum leak after engine warms up.

 

[nola mike]

It does fine in-gear and rough in neutral
As nola mike mentioned it's the shift interrupter. The switch is staying engaged and causes the rough idle. Might need adjusted, lubricate linkage or replaced

Couldn't remember on this engine whether it was cylinder deactivation or complete engine cutoff when activated.

 

[alldodge]

Not complete cut off

 

[ZafSC]

It does fine in-gear and rough in neutral
As nola mike mentioned it's the shift interrupter. The switch is staying engaged and causes the rough idle. Might need adjusted, lubricate linkage or replaced

I removed the switch, it seems to be working. I put the relevant pictures below. (Pictures taken engine not working, shut)

Idling problem 2 - Google Drive

drive.google.com

The only pins on the connector are 1 and 3 used. (2 is not connected anywhere). Normally short circuit, when pressed they become open circuit. But pressing a little does not work, it should be pressed almost all the way down (3/4 almost).
I guess it is working, otherwise (if it were always short because of not pressing enough) than I wouldn't be able to switch gears (ignition not cut off) when engine running, right?

 

[ZafSC]

3 possibilities.
Incorrect IDLE mixture screw setting for a warmed up engine
Idle speed is too low when engine is warmed up.
Intake vacuum leak after engine warms up.

It says there is no idle mixture screw on this engine, all is controlled by IAC, and replacing didn't help.
About intake vacuum leak (checking vacuum hoses and connections for cracks, splits etc) I don't think I can handle this by myself. I am just an amateur hobby mechanic.

 

[cyclops222]

The correct thing to do.

 

[nola mike]

It says there is no idle mixture screw on this engine, all is controlled by IAC, and replacing didn't help.
About intake vacuum leak (checking vacuum hoses and connections for cracks, splits etc) I don't think I can handle this by myself. I am just an amateur hobby mechanic.

A lot of ways to check. Smoke machine on amazon, use propane/carb cleaner and spay around potential leaks (TB, intake hoses, etc) and see if engine speed changes.

 

[nola mike]

I removed the switch, it seems to be working. I put the relevant pictures below. (Pictures taken engine not working, shut)

Idling problem 2 - Google Drive

drive.google.com

The only pins on the connector are 1 and 3 used. (2 is not connected anywhere). Normally short circuit, when pressed they become open circuit. But pressing a little does not work, it should be pressed almost all the way down (3/4 almost).
I guess it is working, otherwise (if it were always short because of not pressing enough) than I wouldn't be able to switch gears (ignition not cut off) when engine running, right?

Knowing the switch works doesn't help with your problem. Issue would be switch staying closed when it shouldn't be. Need to check it installed and see if it's being pressed/sticking inappropriately.

 

[alldodge]

I guess it is working, otherwise (if it were always short because of not pressing enough) than I wouldn't be able to switch gears (ignition not cut off) when engine running, right?

Correct, appears to be working, So long as switch does same when running (nola mike)

Not seeing signs of vacuum leak. Motor goes under heavier load (idle in gear) and idle smooths out. Going into gear would cause the IAC to open more do to load

Be nice if scanner was connected to watch what happens

The one thing would should know but don't is the motor serial number???

If this motor has a flat cap, suggest replacing it just in case. Have had many problems with them over the years and they look great. If it doesn't help keep as spare on board

 

[ZafSC]

Correct, appears to be working, So long as switch does same when running (nola mike)

Not seeing signs of vacuum leak. Motor goes under heavier load (idle in gear) and idle smooths out. Going into gear would cause the IAC to open more do to load

Be nice if scanner was connected to watch what happens

The one thing would should know but don't is the motor serial number???

If this motor has a flat cap, suggest replacing it just in case. Have had many problems with them over the years and they look great. If it doesn't help keep as spare on board

Attached is the sticker on the engine including the serial number..

Serial no - Google Drive

drive.google.com

 

[alldodge]

Yes flat (crap) cap

 

[ZafSC]

Knowing the switch works doesn't help with your problem. Issue would be switch staying closed when it shouldn't be. Need to check it installed and see if it's being pressed/sticking inappropriately.

I guess the switch is working. While the engine running in idle (it usually idles fine when engine is cold, right after start) I unplugged the switch connector, and the engine stopped.

 

[ZafSC]

Yes flat (crap) cap

I replaced the distributor cap and rotor, it seems like it helped a bit. But still, after engines warm up, the idling problems show up more often. As I mentioned, the worst situation is when I am back at the dock, lots of traffic, the engine is warm, I need switch gears back and forth often and suddenly idling stops. Thankfully it always starts when I crank it. After starting, it sometimes gears and running no problem, but sometimes gears and stops. It helps if I gear quickly before idling dies out.

 

[ZafSC]

This folk seemed to have a similar problem, but I didn't exactly understand how he solved the problem. Is there a usage method that I can avoid this happening?

Mercruiser 5.0 MPI idle issues; replaced IAC; bad part? UPDATE **Added Video**

Ever since I bought my 2005 used boat with a Mercruiser 5.0 MPI it's given some intermittent idle issues. The symptoms seemed in-line with a bad IAC. Usually it would just require a restart and I'd go on my way, but lately it started getting to where the boat wouldn't want to start and required...

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