I have an intermittent issue and don't know if this is normal or not. The car is low mileage and has had recent gas and air filter change, and does not burn oil. Most of the time it runs normally, but about every 2 or 3 weeks it begins to get a bit sluggish, which I can quickly remedy by flooring it on a takeoff or causing a downshift, which is always accompanied by a pretty decent (large) black soot cloud, and then the car runs great! Is this normal? It almost feels like something is getting gunked up - and then when I floor it I blow it all out and the car runs normal. I drive the car about 400 miles per week, mostly highway and steady speed. I can live with this, (and the smokescreen can be fun!) but I would like to correct if possible.
What causes this, and what are some potential remedies?

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

Sounds like a sticking EGR valve. You should be able to remove it and clean it out with some spray carb cleaner. Test it with a MityVac to ensure smooth operation.

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Rick Miley
2014 Tesla Model S
2018 Tesla Model 3
2017 Nissan LEAF
Former MB: 99 E300, 86 190E 2.3, 87 300E, 80 240D, 82 204D Euro
Chain Elongation References

mine does the same thing about every 4 months, and yeah, it is fun! my EGR has been disconnected for a long time, and besides i cleaned it thoroughly about a year ago. when yours does it, does the smoke come out ALL at once when the trans shifts up again? or does it come out gradually when you put the pedall all the way down? mine comes out all at once when it finally shifts into 4th, the people behind me usually slam on their brakes. i dont think anything is wrong with it, could be it is burning off alot of deposits, ala "italian tune-up". i dont worry about it.

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1991 300 D 2.5 Turbo, 220k
also in the family:
1981 240 D 185k
1991 350 SD 185k
2006 S 500
2005 SLK 350

Yes, it comes on all at once, usually on a downshift or hard acceleration. I don't mind really, but want to make sure nothing is wrong as I really love the car and want to keep it in good condition for a long time!

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John Gillespie
1988 560sec - 192k miles
2006 CLK500 - 40K miles
1995 E300 - 202k miles

Yeah, go about 40mph an then kick it down for a major carbon burn out, and some head-snapping fun. I try to do this once or twice daily. After a few days of light-footed freeway driving the carbon does really build up. It's amazing.

Mine seems to be getting slightly slower and slower as time goes on (or I'm in more and more of a hurry). My EGR is connected, maybe I'll have to clean it.

Let us know if any other adjustments or cleanings give you good results.

-m

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Now:
2018 Tesla Model X
1999 S500 Grand Edition 164k
1992 300D 2.5 Turbo 287k
2005 E320 4MATIC wagon
1991 Alfa Romeo 164L 99k (sleeping for a while)

Then: 96 Lincoln TC, 93 Lincoln TC, 87 560 SEL, 87 300 SDL, 80 300D, 89 560 SEC