So I have a bit of a head-scratcher courtesy of my 2012 ML350 Bluetec. I've been through a handful of posts with people having the same concern as me. There's no MIL, and no shaking/shuddering/stuttering, but there's still poor acceleration. Mine's not a consistent problem though. The reason I'm posting is that there seems to be extra pieces to my puzzle. This will be meandering, so I apologize in advance, but I try to include details:

Early in the summer this year I drove into town and arrived at my destination to find the radiator fan on full blast. Jet engine just right there under my hood. The temp read pretty low, even for early summer with the a/c on. I turned the car off, and turned it back on again, completely normal. It didn't do that to me again until this past week. One rainy afternoon, I was on the highway for one exit-- maybe an 8 mile trip from my home and I got to where I was going and it was doing that fan trick again, this time the temp gauge was still straight down at 40*C. I turned it off, turned it back on, and the fan was normal. This time, however, the acceleration problem hit. It had started raining harder, and honestly I couldn't tell if the acceleration thing was a problem or a feature...

Well, today, I drove a good hour to get where I was going. Highway the whole time. Between the road noise and the music I couldn't tell where the fans would have started, but when I finally slowed I could hear them roaring. I pulled over, parked, turned off, and turned it back on. Since I had such a concern from last time I tested acceleration in a parking lot. Can it accelerate? Well, as is reasonable for a public parking lot. I'm curious, not reckless. Anyway, I'm in the running car, in line waiting for about an hour or so and the temp is creeping up. 50ish*, then 80*, then about 100*. No fan noise this time... Getting back on the highway turned out to be terrifying because it only accelerates like some little old lady is on her way to church. I try using the paddle shifter to downshift and maybe trick it into doing my bidding. Nothing. It doesn't even say what gear I'm in and I'm unable to manually select a gear. No matter where the pedal is, it won't seem to downshift either. I couldn't tell you what the RPMs were doing at any given time-- the tach is broken.

I get home, get mad about it, but 90 minutes later I have to leave again. It drives like nothing ever happened.

From other threads I read, it sounds like the fuel pump is the culprit. I'll be honest, I didn't read far enough to find out if that's the in-tank pump or the diesel pump... I'm just a little skeptical I would be having the same problem if it's not letting me paddle shift and is also preceded by electrical quirks. Others have said a clogged/dirty EGR can have repercussions that include loss of power and the transmission shifting funny (I'll be honest idk how long ago I read that, or if it was even on this forum). Any thoughts, or do I just have multiple problems?

 

Swirl flap motor is acting up. Sometimes it stuck open and sometimes it stuck close which will cause the symptoms of poor acceleration. Check your intake turbo seal and see if there is oil on top of the swirl flap motor.

Check out the video above. If there no CEL, it may take sometimes to find out the issue(s).

 

good video, very informative...!

 

This!

It's clarified a lot of questions I had about the seals etc. Thx so much for posting the link

 

Thank you so much for that video!
The car's coming up on 100k miles. I've been walking between raindrops as far as maintenance items go; I guess I was overdue for something. The video mentions a CCV gasket on the Y-pipe. Is that different from PCV? I do also intend to replace that coming up here

 

I think they r the same. I will get those 4 seals replace and 2 air intake box seals as well