Quote:
Originally Posted by WilcoJunoHotel
Mine has done it since new - almost 2K miles now. Barely perceptible on mine though - just a little lumpy idle for a minute or so then it smooths out. Only on cold starts when it has been sitting overnight. I am guessing it is the fuel injection system. When I take mine in for the first free oil change I will have them look at it.
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I notice a bit of engine roughness -- but nothing that has me thinking it is a problem -- upon/shortly after a cold start of my 230xi and M2.
I believe it is the engine reacting to an overly rich mixture done on purpose to supply excess fuel to the converters to get them to warm up quicker.
The engines smooth out as the elevated cold idle RPMs drop to near hot idle RPMs concurrent with the engine controller going closed loop mode and the overly rich mixture gives way to a leaner mixture.
My 2 BMWs are not the only engines to manifest this bit of roughness after a cold start. It has been common with engines as far back as I can recall. (In all from memory 17 engines from a 90hp VW TDi to a 707hp Hellcat.)
Now two times two different engines manifested enough roughness over and above what could be considered normal (and in one case the CEL came on and misfire error codes were logged) at cold start to have me suspect a problem.
One engine was in the the VW TDi. Long story short the coolant sensor was bad.
The other engine was in my 996 Turbo. I "fixed" the CEL/misfires upon shortly after a cold start by just cutting short how long I let the engine idle after a cold start. Oh, the engine never misfired or acted up at any other time.
Some time (years) later I found the cold misfires were no more. But I had not done any engine work to address these.
I'll add with at least two cars I know of: Hellcat, Scat Pack; lack of sufficient use had both cars manifest odd symptoms upon/after a cold start. No misfires, rough idle, but issues of an electronic nature. Car apps that hung when I tried to load them. Goofy LCD displays. And the more disturbing symptom was the Hellcat its +paddle would cause a *down shift* rather than an up shift. No CEL but shop foreman found several proprietary low voltage error codes. He applied several firmware updates and upon learning of low voltages I drove the car more often.
No more problems. (Oh I drove the Scat Pack more often too and no more problems.)