Of course she can, with this forum's help - or at least, she will try and try again!

This is for my W124 91 300E, 195K miles, which I recently got back after 5 years (long story)...

Just had new brakes/front end work done, new tires, changed oil/air filter, new radio - now for the harder stuff...

Check engine light on, idles rough, auto trans slipping for starters, but so much faster (and much more complicated) than the 240D

#1 Behind the oil dip stick, there is a narrow hose that goes under the air filter to a bigger black hose between the air filter housing and the ?

It was brittle and broke when I was changing the bigger black hose (old one shown in pix) - what is the purpose of this narrow hose and can I get a generic hose (from CarQuest, for example) to replace it with? Or is it a special item?

#2 When the transmission slips, it usually happens when going up an incline, automatically shifting to a lower gear, revving up to between 3 - 4.
As a remedy, I shift into N, let it rev down, then shift back into D. Is this practice doing more damage?

#3 By idle rough, I mean sounds uneven, like there is an air blockage or ??? I bought new spark plugs to replace (I had changed them myself 5 years ago), but I'm guessing there is something else going on?

Attached Thumbnails

 

__________________
1991 300E 124.030 103.983KE 722358 03 412178
207K

1979 240D 123.123 250K (Project car)

2000 Ford Ranger, 187K

2015 Dodge Ram 1500 EcoDiesel 37K