Hi,
I recently got the following issues from my 2017 GLS450 - 115K: A very rough lumpy idle, white smoke from the exhaust and the engine will not rev smoothly at any speed. An OBD tool reports, the following faults:
P0505 - Idle Control System Malfunction
P0302 - Misfire in Cylinder 2
P0305 - Misfire in Cylinder 5 (this comes and goes?)
P300 - Random Multi Cylinder Misfire.
Reset them will not work at the codes are stating the are "PERMANENT" - I guess they will self purge once the issue is no longer present!

I have replaced all the plugs and switched the coils that are reporting a misfire, but the misfire stays at Cylinder 2, Cylinder 5's misfire comes and goes?
Can anyone help with the following: some sites state to clean / replace the IACV - where is it, doe's this vehicle even have one? Will cleaning the trottle body help?
Any help will be greatly appreciate....
Thank you
Sam

Cylinder specific misfires are usually traced to either ignition components, fuel injectors, or their respective wiring and controls. Less frequently they can be caused by valve train problems.

Thanks for the insight John

White smoke, rough idle and misfire are consistent with coolant in the combustion chamber. Start the path of diagnosis for a failed cylinder head gasket.

- bubbles in the coolant reservoir?
- chocolate milk film/sludge under the oil fill cap?
- sweet smell from exhaust?
- coolant level dropping over time?
- "washed" piston face or spark plug?
- low compression on any cylinder?

Thanks for the input "Chassis" but of the items you described non have been noticed or seen, to date, with the exception of the last one, i have no means to test this, but running a test with the scan tool with live data reports no anomalies on any piston? This is somewhat contradictory considering it also reports a misfire on cylinder 2!

- bubbles in the coolant reservoir? - NO
- chocolate milk film/sludge under the oil fill cap? - NO
- sweet smell from exhaust? - NO or not percievable by me?
- coolant level dropping over time? - NO - coolant look s normal with no signs of level change of contamination
- "washed" piston face or spark plug? - Replaced plugs but old plug@ cylinder 2 had a cracked and broken insulator and looked grey.
- low compression on any cylinder? - TBA

Sam

That spark plug doesn’t look great. It looks muddy to me.

That's not good...

Sometimes that is caused by destructive detonation, (or someone dropped the plug and used it anyhow) which can cause all sorts of other problems in that cylinder. I'd want to do a boroscope inspection on that one.

Broken plug could be caused by water in the combustion chamber.

Do you think you have a failed cylinder head gasket?