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If I didn't have Star Diagnosis with DAS I could say that the problem is solved. The floating is no longer bother me, at least not to the unarmed ear. You don’t hear any anomaly or floating on idle speed. The solution involves replacing some parts as well as coding. But if you arm yourself with a DAS, you can see that the lambda control is still “floating” on a very “correct” sine wave. Yes, I have been able to make the engine respond smoothly to these changes, but the cause itself is not eliminated. I'm assuming the problem is the catalytic converters. I will try to find used catalytic converters with low mileage and change them. I will then report back here with the results.
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.
Last edited by E55Greasemonkey; Nov 2, 2025 at 06:22 PM.
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.
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.
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.
Last edited by E55Greasemonkey; Nov 30, 2025 at 12:43 PM.
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.
Mercedes SLR McLaren 722 S Is Extremely Rare Example Modified by McLaren
Slideshow: A one-of-one U.S.-spec Mercedes-Benz SLR McLaren Roadster became even rarer after a factory-backed transformation at McLaren's headquarters.
