Mercruiser 350 MAG MPI -2002 need full throttle to start warm engine-gctid394561

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

Hi,

I have a problem with my Mercruiser 350 MAG/MPI -2002 (mounted in a Bayliner 2855).

When the engine is cold, it starts within 1-2 seconds with the throttle lever in idle position.

When the engine is warm and have been off for 2-15 minutes i need to give almost full throttle to start it. Once it has start, it runs perfect.

Anyone who have had the same experiance?

Can the problem be a defect temperature sensor?

/Robert

[Davidlyne Guru Find all posts View Profile Close Davidlyne]

I have a 5l MPI and HAD a similar problem. Perfect starting when cold but a real dog when hot or warm. I had the mechanic look at it and it was the "idle control valve". I think this is the right name for it. It is a silver part that sits on top of the engine. You can see it with the plastic cover off the top of the engine. About $450 later all is now perfect. I was also told it is a common problem with the mercruiser and the workshop had plenty of these valves in stock.

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

Davidlyne wrote:
I have a 5l MPI and HAD a similar problem. Perfect starting when cold but a real dog when hot or warm. I had the mechanic look at it and it was the "idle control valve". I think this is the right name for it. It is a silver part that sits on top of the engine. You can see it with the plastic cover off the top of the engine. About $450 later all is now perfect. I was also told it is a common problem with the mercruiser and the workshop had plenty of these valves in stock.

Did you have a good idle RPM once the engine was running?

Both when started from cold and hot condition?

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RobertL wrote:
Hi,

I have a problem with my Mercruiser 350 MAG/MPI -2002 (mounted in a Bayliner 2855).

When the engine is cold, it starts within 1-2 seconds with the throttle lever in idle position.

When the engine is warm and have been off for 2-15 minutes i need to give almost full throttle to start it. Once it has start, it runs perfect.

Anyone who have had the same experiance?

Can the problem be a defect temperature sensor?

/Robert

Robert: I'd suggest that you try to find a friend who has the diagnostic tester that will check all of the systems on your 350 Mag engine. Maybe you'll be lucky and the fix will be easy! Good luck. Griff

[Davidlyne Guru Find all posts View Profile Close Davidlyne]

RobertL wrote:
Did you have a good idle RPM once the engine was running?

Both when started from cold and hot condition?

YES. It was perfect when I finaly got it started, and it ran perfectly. (Actually, now I think about it, it was idling about 150rpm higher than it does now at idle)

The mechanic isloated the problem with the Mercruiser tester, wasn't a hit or miss guess. As I mentioned, he said it was a common problem.

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It may be your IAC (Idle air controller) has gone bad. It's between $65-95 and does have a reputation for causing these symptoms.

[Davidlyne Guru Find all posts View Profile Close Davidlyne]

Nehalennia wrote:
It may be your IAC (Idle air controller) has gone bad. It's between $65-95 and does have a reputation for causing these symptoms.

That sounds like the part I had replaced. A lot more dollars than that over here though!!!!!!

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

griff wrote:
Robert: I'd suggest that you try to find a friend who has the diagnostic tester that will check all of the systems on your 350 Mag engine. Maybe you'll be lucky and the fix will be easy! Good luck. Griff

The only option for me is to rent a tester. But that will cost almost as much as buing a new component. So I will test to replace it.

Thanks,

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

Thanks for all input!

I have ordered a new IAC and hopefully I will know this weekend if it worked

/Robert

[Davidlyne Guru Find all posts View Profile Close Davidlyne]

You MAY still need the "tester" as the error code on mine had to be reset after the part was replaced!!!!!

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Davidlyne wrote:
You MAY still need the "tester" as the error code on mine had to be reset after the part was replaced!!!!!

is not need for tester, i replaced mine last week took out for long spinn and all went fine,

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RobertL wrote:
Thanks for all input!

I have ordered a new IAC and hopefully I will know this weekend if it worked

/Robert

with your IAC hope you ordered the gasket and the muffler because they not are included.

I changed mine last week in my 2004 350MAG MPI and all is fine now

[Guest Close Guest]

Hi Robert, I have the 350 MPI in my 2452 had the same problem, progressively got worse, Mine was something as simple as the timeing, Is it kocking or down on power? once it fires do you have to rev it to clear it out?

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

DEK wrote:
Hi Robert, I have the 350 MPI in my 2452 had the same problem, progressively got worse, Mine was something as simple as the timeing, Is it kocking or down on power? once it fires do you have to rev it to clear it out?

Hi,

Actually it consumes a little bit to much fuel at cruising speed, 50-70% more than other that I have compared to. And yes, once it has fired up I have to keep rev it for a few seconds before the engine idle correctly.

I have not noticed any knocking.

Is the timing adjustable? Was it a sensor problem?

[RobertL Frequent Contributor Find all posts View Profile Close RobertL]

I have now changed the IAC but it did not fix the problem.

Have now noted the follwing:

Cold engine: Perfect start and idle.

Warm engine, turned off for approx. 1-3 min: Perfect start and idle.

Warm engine, turned off for 5 min or longer: Need full throttle and be cranked for 5-10 sec to fire up. When some rev for a few sec before the idle is good.