Uneven Idle Speed

[Obsidian]

My '08 Yammy 150 continues to give me cause for inquiry, the tickover varies over the course of a day. I try to set it to 600 RPM, but sometimes (after a while) it drops to stalling and other times increases to 900.

Any ideas on what I can check, could the idle screw be slipping with vibration?

[boristhebold]

Try changing the spark plugs, cheap fix if it works, one of them maybe worn which might give erratic firing.

[boristhebold]

Try changing the spark plugs, cheap fix if it works, one of them maybe worn which might give erratic firing.

[boristhebold]

try changing the spark plugs

[A1an]

You REALLY want him to change those plugs don’t ya.

[Lee argyle]

Originally Posted by A1an

You REALLY want him to change those plugs don’t ya.

3 plug changes.............just to make sure

[Orwell boy]

Have you considered taking it for a service at your local Yamaha main dealer ? ,or maybe the command link software off ebay may help if pre 2012 ?? . it may turn out an expensive service may turn out cheaper than changing a load of unnecesary bits .

[Obsidian]

Thanks Boris and Orwell

Plugs are definitely worth a go, I think she is still running a bit rich from the TPS saga so they will most likely be sooted up at the very least.

Got the software and doing regular ECU dumps, but nothing indicative in that so far though.

She has been seen by no less than 5 dealers in the last 18 months and none have had any good ideas about the uneven idle, most conclude that its not a major problem but I would really like to iron it out.

[Fender]

Have you tried changing the spark plugs.............................?

Might be the induction system, a small air leak will give you a fluctuating idle which could vary with engine temp ( expansion etc ). Carefully squirt some easy-start around the air intake system/inlet manifold, if the revs change there's your problem

[Obsidian]

Originally Posted by Fender

... squirt some easy-start around the air intake system/inlet manifold, if the revs change there's your problem

[jeffstevens763@g]

Originally Posted by Obsidian

My '08 Yammy 150 continues to give me cause for inquiry, the tickover varies over the course of a day. I try to set it to 600 RPM, but sometimes (after a while) it drops to stalling and other times increases to 900.

Any ideas on what I can check, could the idle screw be slipping with vibration?

is it a fuel injected engine

[boristhebold]

Originally Posted by A1an

You REALLY want him to change those plugs don’t ya.

was an issue with the website

[Obsidian]

Originally Posted by jeffstevens763@g

is it a fuel injected engine

Yes it is

[jeffstevens763@g]

Originally Posted by Obsidian

Yes it is

it might not be related but i had tick over issues with my suzuki very low hours went to the dealers 6-7 times couldnt find anything,tested, filters, plugs the usual changed. threw my dummy out told them to strip it down or send it back it was then they found water globules in the fuel lines and IAC valve blew it all out now sorted.
i dont know where the water came from and it wasn't much i'm now using fuel set which gets rid of small amounts of water the supplier told me around £10 for a small bottle which goes a long way.

[Obsidian]

Thanks Jeff, I do use Fuel Set fairly often. Good tip though

[wgc851]

IAC valve?

[jeffstevens763@g]

Originally Posted by Obsidian

Thanks Jeff, I do use Fuel Set fairly often. Good tip though

As below could be a dicky IAC valve good luck

[Callum B]

Hi fellas,

Ive got a 4 stroke 3.5 hp tohatsu auxilliarly thats running rough.....this lockdown business has given me some time to have a gander.

Symptoms:
1. It doesnt idle well....the only way it will tick over consistently is to raise the tickover speed, higher than it should be.

Reducing the tick over results in it gently getting slower, til it stalls.

2. Revving the throttle in neutral can sometimes stall, but always hesitant before pick up. Once picked up, it runs fine.

3. Very small adjustments to the tick over speed result in revving too high, or very slowly decreasing on revs, til it stalls.

......carburettor low jet, i hear you all scream, but ive had it in bits, and although there was minimal sediment in the carb, it all blew through fine, after i cleaned the high jet, bowl and needle valve.

The spark plug looks good.

The engine is second hand to me, and never run properly at low revs since i got it, but it is a low hours engine, in good nick.

I know its fuel / air related, but my amateur mechanical ability has run out of ideas.

I was going to get the carb electrosonically cleaned, but it could be a defective carb??.... over my paygrade now!!

Does anyone have any experience of this, or suggestions how to resolve??

Thanks.

[diver 1]

On the Yam the OP refers to I'd place a bet on the IAC valve. I've had ones that bench tested to factory spec appear fine on the voltmeter and work fine under diagnostics yet play up on the rib. Worth seeing if you can perhaps even 'borrow' another one for a quick trial to see if that cures your problem. Shouldn't be too difficult to do

[Callum B]

Thanks diver.....i think im the only guy in the world that has one of these....getting another "iac" valve is gonna be tricky!!......whatever an iac valve is??....intake air c..c...colostomy??.... sorry....im not fully outboard techy!!


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