1991 300E - runs rough, can she fix it?

[mbzr4ever]

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?

[johnflight1]

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.

[mbzr4ever]

Originally Posted by johnflight1

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.

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.

[johnflight1]

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

[mbzr4ever]

johnflight1,

Just got back from CarQuest, and they told me it was a part, not a hose, that had to be special ordered.

I'm still going with replacing it as a "hose", as you mentioned.

[lorainfurniture]

First thing to address is the check engine light. Most times on these cars the only thing to trip the light is the o2 sensor. The car is likely running very rich or lean.

Next is to give a full tune up. Cap, rotor, wires and plugs. I would check the vacuum as well. You should have a min of 12hg, ideally 15-16 at idle.

That hose that connects from the airbox to the valve cover won't help your running issues, but should be addressed anyway.

[mbzr4ever]

n/m, checking with pelican parts.

[Ferdman]

mbzr, your local MB dealer can sell you the proper hose/line that you need. It will be high quality for that specific application.

[mbzr4ever]

Ferdman,

Yes, I have an inquiry with pelican parts; if they don't have, I will order from dealer.

EDIT: PP had; ordered.

[mbzr4ever]

Originally Posted by lorainfurniture

First thing to address is the check engine light. Most times on these cars the only thing to trip the light is the o2 sensor. The car is likely running very rich or lean.

Next is to give a full tune up. Cap, rotor, wires and plugs. I would check the vacuum as well. You should have a min of 12hg, ideally 15-16 at idle.

That hose that connects from the airbox to the valve cover won't help your running issues, but should be addressed anyway.

Lorainfurniture,

Search can't seem to handle "o2" because it is too short, is there something else I can search by? Maybe the word oxygen sensor or ?

[lorainfurniture]

Originally Posted by mbzr4ever

Lorainfurniture,

Search can't seem to handle "o2" because it is too short, is there something else I can search by? Maybe the word oxygen sensor or ?

Try google search "300e check engine light" or "w124 check engine light"

I don't remember where I read it, but it made sense when I read it. The check engine light is always emissions related (please someone correct me if I'm wrong), And the o2 sensor is about the only electronic emissions device on the car.

[Ivanerrol]

Originally Posted by johnflight1

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.

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.

[mbzr4ever]

starting here with fault codes:

http://mbslk.de/files/artikel/r170_fehlercodes.pdf

[mbzr4ever]

Ivanerrol,

thanks for the picture, very helpful.

Tried searching for the (transmission) regulator at pelican parts - can it be called something else?

sigh (I miss driving with manual transmission already...)

[Hirnbeiss]

When you say the tranny slips, is it possibly only downshifting? i.e, is it staying in gear, just a lower one?