Anyone know how to find out why the 5g tranny doesn't know when to downshift when I go WOT. I recently changed the spark plugs because I thought that maybe with it being 12 years old and 180K km's (110K miles) it probably had original spark plugs. I changed them and they appeared to be original. I also tried the transmission relearning, but it didn't do much. There are times when the car feels perfectly responsive and as fast as it should be (even before changing spark plugs) But a lot of times, when I go WOT, it stays in gear and feels pretty weak, and should have downshifted and had a lot of room to rev before redline (I'd even expect a E350 to be faster) There are no check engine lights. Has anybody had similar symptoms, and did you find out what is was? Or any tips on what to check?

Try replacing the pilot bushing or the transmission connector. It ends up wicking up transmission fluid and things act strangely. Or get it scanned for transmission specific error codes. You might not get a CEL lights for transmission error codes. Or it could be the conductor plate going. But first try the connector, it's cheap. Also did you change the transmission fluid? Supposed to do that every 40k.

https://www.fcpeuro.com/products/mer...tor-2035400053

You can get a case of 12 quarts of Shell ATF 134 for about $60 from a shell distributor.

https://www.shell.us/business-custom...r-locator.html

I'm going to try and find out about the fluid, I was thinking about doing that, and thanks for the tips about the other parts. Really hard to find decent mechanics where I live, so going to need to figure out where to have it scanned. I tried searching for an indie around where I live, and there aren't any (basically)

I purchased the car recently with the understanding that the 5 speed was bulletproof and reliable, and used in so many Mercedes for a long time. I didn't realize how many issues they can have, and just to find things out requires expensive diagnostics.

You should just get a code reader that can do MB specific codes. If you search the forums, there's lots of them out there, icarsoft, autel Diaglink, carly, icarscan, etc. Most are in the $100-$200 range.

The diaglink you can get for $89.