Hi. Replacing which parts resolved the unstable idle speed problem?

 

I'm having a lumpy idle on my 2010 m273 with only 72k miles. My idle mixture adaptations are a touch high , meaning fuel is being added. This typically means a vacuum leak,and spraying brake cleaner at the very bottom front of the intake manifold causes the engine to stumble slightly. There appear to be short vacuum hoses and switchover valves down there, but difficult to see or access. I'll be removing the air injection pump for a closer look and update you all on what I find.

 

those air tumble flap actuators are a sick joke - as you can't see most are lubricated and thus snapped off externally - then the detritus inside the inlet manifold they operate is designed to come off and get ingested destroying the engine

stuck in the low rev position you miss a lot of top end grunt - misfires could be coil sticks giving up or the inlet manifold doing what mercedes designed it to do

 

There are tests in Xentry to activate those dash pots and you can watch them go through their travel. It's also a good time to shoot some white lithium lube or similar on the joints during operation.

 

but you can't see if inside the bits that matter are sill attached - many are just hanging on before engine destruction awaits all of us

even if happy to accept performance and economy reduction - the catastrophic injection of rubbish into the combustion chamber is not a good idea....

used to be big bits of brass on BMW tractors (swirl flaps) - even when they moved to plastic - it still destroys the engine when ingested

 

Below is something I do whenever I have the air box off my M272 engine.

I had also replaced the sealing ring due to the metal wire clamp attached to the maf fitting loose and sloppy over the top of the air box, after the new sealing ring it clamped on to it tight and could feel it snap on into place.

 

@Plato Did you found the problem?

 

the tumble flaps actuated by a load of stupid linkages hiding at the front of the inlet manifold - are an issue - you can pop off a vac pipe and suck open with a tube to see if they move / function - three actuators if I remember correctly. You can get bits of junk trying to repair snapped external linkages - but the reality is inside the inlet manifold is a load of junk waiting to destroy your engine - new manifolds aftermarket are readily available - peirberg I think, might be OEM out the supplier back door around $500

for USA market once upon a time there was a free manifold as the early ones were faulty.... don't believe any in europe had one

that said - unless inside bits already been ingested / failing I doubt this will cause a misfire

 

Update: I sent my fuel injectors to Fuel Injector clinic to be cleaned and flow checked. One injector had low flow compared to others after multiple cleaning attempts. They suggested I replace that injector, which I did with a new OEM injector. Great service by them as they also credited me the $25 fee for that injector which I was able to apply to the new one. I also removed the intake manifold and smoke tested it with no leaks found. I suspect the change in idle while spraying the brake cleaner was the fumes/over spray being ingested by the MAF since I had the air cleaner assembly off the car. I reassembled everything, reset mixture adaptations and raised the idle 100rpm in both park and gear with Xentry and this seems to have resolved my idle issues. Xentry compression test passed with 10 rpm difference in one cylinder. I will use some BG snake oil piston ring cleaner on my next oil change as I've seen that test improve afterwards on m272 engines I own.

 

Excellent advice!