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

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

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:eek::eek::eek:

#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?

small vacum line
 

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.

replacement
 

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

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.

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.

n/m, checking with pelican parts.

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

Ferdman,

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

EDIT: PP had; ordered.

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.

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.
http://farm4.staticflickr.com/3148/2...1908df7e_o.jpg

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.

starting here with fault codes:

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

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...)

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

Doesn't happen all the time; at first I thought I had a 4 matic or similar, and didn't know how to drive it properly.

Usually happens when going up an incline - it will downshift to like 2nd, and rev high (3 to 4 rpms)
Or it will start in first, or after 1st/2nd, won't shift to a higher gear and will continue to rev in the 3 to 4 rpm zone.

Is the control pressure cable adjusted to the zero-slack position?

of course you also have to ensure it has enough ATF too.

Yes, the ATF level was the first thing I checked.
Will have to research the control pressure cable.

Fault codes are coming up as:

11 Air Injection system
16 Exhaust Gas Recirculation (EGR)
17 Oxygen Sensor signal
18 Current to Idle speed signal

Would cleaning out the idle control valve remedy 18 (Current to Idle speed signal)?
Just saw a video on this, using mineral spirits.

Doing more research and MAS keeps coming up as a possible issue, now remembering the AC/heater/fan doesn't work.

Also, how do I know if I have the 717.4 or 722.4 transmission?
B2 piston replacement also looks to be in order?

sigh. now I'm really missing my old 240D with the manual everything.....

Cleaned out the idle control valve, made no difference.

Tried to change the spark plugs, but they were too tight to get out - was afraid of breaking them, so I left them alone.

Guessing I have the 722.4 transmission.

Checked the fuse behind the battery, was ok.

Any ideas on what I should check next?

O2 sensor?

Btw the plugs are a must, one way or another. Try heating them and then putting an ice cube on it right away. Spark plugs on the m103 need to be changed every year/ 16,000 miles.

lorainfurniture,

I didn't try the heat/ice - I shot some PB blast into the area, hoping one would budge...but nothing.
Heard horror stories of broken spark plugs, and didn't want to risk further.

I had the new plugs, and even that special torque wrench ready to go.:(

Should I look up cleaning the O2 sensor or just replace it?
Fortunately, I don't live in a state that the car would have to pass an emissions check.

Pull your passenger side carpet and you will find the harness for the o2 sensor. It should give a reading from .03-.07 I believe.

You think the spark plugs are tight? Wait until you try cranking on the o2 sensor.

Finally changed the spark plugs.
Pulled the carpet but nothing obvious sticks out like the o2 harness:confused:

Typically the Oxygen sensor connecting lead is blue with a black grommet where it penetrates the driveshaft tunnel. The grommet is likely just under the carpet edge on the side of the tunnel.

:rolleyes:So I've been working on the 240D and the Ford in between, but while waiting for parts, decided to drive the 300E again.

I stopped at the point of changing the O2 sensor, debating if I should just clean it or replace it - but now I have a new issue:

The check engine light is off, but the ABS light is ON!
Hard to start, idles very, very rough, sometimes almost dies or dies.

***Weird, before it was revving too high, now too low*****

The abs system is powered throughout the OVP relay. It is a silver relay with a red top located behind your battery. It usually has 1 fuse on top, or 2. Sometimes the whole relay goes bad (bad solder joints) and must be replaced. It typically causes the abs light, and shuts down the "E" part in you "cis-e" fuel system.

CIS-E stands for continuous injection system, electronic assist. The electronic stuff really does work at keeping idle.

Thanks for that info - I pulled a red 10V fuse from a device from behind the battery.
The fuse looks intact; are you saying the rest of the unit could be defective?

This is what I order, correct?
http://www.pelicanparts.com/catalog/SuperCat/3321/MBZ_3321_ELSWCH_pg5.htm#item24

That looks like the correct unit.

In looking at the engine again, I noticed the blower strip fuse was gone - no wonder the fans wouldn't work!

Also, found this to be helpful:
http://www.peachparts.com/shopforum/diy-links-parts-category/209638-ovp-relay-over-voltage-protection-links.html

The hose - this hose will make a serious vacuum leak, and will absolutely make the car run rough and/or stall. There is a specific part for it, a molded hose with two 45 degree bends in it. I have found that fuel line hose works fine in that spot.

Do check the OVP relay, it will cause stalls, inability to idle, and the ABS light to come on, among other things. Kind of a notorious part really.

Check for dubious repair attempts. Often when there is something like a bad vacuum leak, instead of fixing the problem, people tend to do something else to compensate. If you've fixed a problem and now the car runs worse, do look for hack repair attempts.

Thanks to everyone who suggested changing the OVP!

This cured the non-starting problem, and a lot of the rough idle.
The related tranny shifting problem has gone away, maybe.
Haven't given it a real test run - probably still going to have to replace or clean the O2 sensor.

update: the old OVP caused the tranmission shifting issue, and that has gone away.
Still need to replace or clean the O2 sensor, but no real urgent need to do that right away.

Changed the O2 sensor yesterday, and noticed the check engine light was off as I started to drive.

Darn, if the light didn't turn on again, after about 15 miles.

Checked the code when I got home, and there was 17 again, as if I didn't change anything.

:confused::confused::confused: