lumpy Idle M42

Post Thu Feb 05, 2015 1:17 pm

Hi Guys,

My car (318IS M42) has started with a Lumpy Idle. Sometimes its fine and doesnt seem effected. But other times it runs lumpy and feels like there's a slight delay in throttle response if I put foot down even whilst stood still.

I have to say also the car smells like it is running rich.

Any ideas on what could be causing this ?

Thanks,
Lee

Post Fri Feb 06, 2015 1:09 pm

Post Fri Feb 06, 2015 1:30 pm

Air leak somewhere? How do the breather pipes look? They can perish and cause air leaks.

Post Fri Feb 06, 2015 1:34 pm

They don't seem too bad, Need to check ICV really haven't looked at that yet.

Post Fri Feb 06, 2015 2:20 pm

ICV doesn't cause a lumpy idle. It may cause a low idle speed, however, that then might be lumpy because it's low (and you're two cylinders short of a 'proper' engine).
Lumpy idle, hesitation on acceleration, and a 'rich' smell, are all symptoms of a weak fuel mixture, which is likely to be caused by a combination of one or more minor air leaks into the intake system, as said above, and injectors overdue for a rebuild.
The 'rich' smell is caused by mixture which is too weak to ignite, which then passes straight through the engine and out of the exhaust.

Post Mon Feb 09, 2015 1:29 pm

I love my 4pot

got some nice potential! I will have a detailed look into it this weekend coming.

It weird sometimes I idles at 600 and try's to cut out because its too low, now its decided to idle at 1300.

Its so random what it decides to do.

Cheers,
Lee

Post Mon Feb 09, 2015 1:56 pm

This revised description of the symptoms sounds much more like it could be a sticking ICV.
My comments on the four pot engine are because the design of a four cylinder engine is fundamentally flawed. It is an 'unbalanced' design that produces unwanted forces and requires the inertia of a flywheel to actually make it run. An inline six cylinder engine (and a V12) is as good as it gets as regards unwanted forces, and the crankshaft is always being powered by igniting fuel.

Post Mon Feb 09, 2015 9:28 pm

If you take off the rubber inlet hose from the AFM you will be able to see the butterflies in the throttle body, make sure they are able to close completely when your foot is off the pedal.

Post Tue Feb 10, 2015 1:10 pm

Thats an interesting fact Brain, I will have a proper look this weekend and everything I can regarding it. I have seen a perished hose which will need changing.

But I don't think its the cause of this lumpiness.

Cheers guys.