the small line comes from the fuel accumulator if the diaphragm were to break the fuel would go thru this line to be recovered into the air inlet system.any fuel smell in this line would indicate a bad fuel accumulator.

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg

Thanks for that info - it sounds like it works as a back up device and doesn't have to do with contributing to a rough idle.

It's probably fine to replace it with a substitute hose, I presume.

Didn't notice a gas smell, but will double check when replacing the hose.

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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

I buy the plastic vacum line in 5' or 10' lengths from peach parts ,ebay or ******** az .you go thru alot of it on these cars it breaks like uncooked spagetti! I use a little crazy glue to hold it in the rubber hose ends it goes into because those are usually old and lose their elasticity I noticed they kept falling out of the rubber hose ends,till I got around to replacing those also. It is like opening a can of worms once you start touching these old brittle things

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88 W124 3.0
96 R129 119eng
06 ML350
98 ML320 sold
02 CLK55 amg

That would be fuel regulator not accumulator. The accumulator is back near the fuel pumps.

The only function that hose performs is that if the fuel regulator diaphragm breaks fuel will leak through the tube back into the air-box and not onto hot parts of the engine and potentially the fuel catching fire.
I have previously just used a piece of small diameter fuel hose to extend the vacuum tube back into the larger hose between the valve cover and air-box. This tube has no effect on the running of the engine whatsoever.
You can see in this image the extensions I put on a regulator tube on another car.


Misfires - as LorainFurniture has pointed out are 85% due to electrical. Plugs, dissy cap, rotor and leads. Buy good quality parts - OEM Bosch or Beru and these will last a long, long time. Be careful of Chinese made Bosch substitutes. These parts are expensive but worth it.

The issue with your transmission maybe the regulator located on the side of the tranny. I say maybe hopefully and not an internal tranny problem - otherwise a rebuild is in your life.