W114 rough idle

1968 - 1976: 220, 220D, 230, 230.4, 230.6, 240D, 250, 250C, 250CE, 280, 280E, 280CE, 300D
Post Reply
S2rka
Posts: 4
Joined: Wed 18 Jul, 2018 2:56 pm
Model you own: w114
Region: New South Wales
Location: Sydney

W114 rough idle

Post by S2rka » Wed 18 Jul, 2018 7:15 pm

Hi everyone!
Out of nowhere, my ‘73 250 started idling a bit rough. Felt a bit funny starting it up too. Needed few more taps on the accelerator pedal to start up instead of a normal single tap.
Nothing unusual when driving around, just when stopped at the lights it started shaking and vibrating like crazy like it’s going to die.
Been checking all the vacuum hoses etc, but can’t find anything besides missing a breather hose going to the top of the intake manifold between the carbies. Replaced that with no changes.
Infact, theres one 25cm long and about 4mm wide vacuum hose going from the intake manifold towards the firewall and not actually leading to anything. At a closer look it seemsed like the end of it was a bit expanded so I would think it should end up sumewhere, but can’t find anything. Any ideas what it could be, or it even cause any of the issues I’m experiencing.
Hope I didn’t sound too confusing.
Any help is much appreciated!
Adding few photos to explain myself a bit better. One of the vehicle as well as it’s my first post here.
Cheers,
Henri
You do not have the required permissions to view the files attached to this post.

User avatar
Bartman4800
300 SLR
Posts: 1985
Joined: Fri 10 Oct, 2008 12:10 am
Model you own: w111
Location: Perth WA

Re: W114 rough idle

Post by Bartman4800 » Thu 19 Jul, 2018 11:02 am

If you hang a vacuum meter to your intake manifold, you might be able to determine it is a vacuum problem.

The hose might be for the central door locking system?

Could it be your brake booster is punctured and drops the vacuum?


Bart
1963 220 Sb Sedan "Kermit" (Australian Assembly)
1960 220 Sb Sedan "Zum Schlachten" (Early German Assembly, with a torsion bar spring for the bonnet) - Stored in Country WA
1981 Subaru Brumby 1.8 with Weber and 5-speed box "little utie" - Sold to another enthusiast!
2006 Ford Focus "daily driver"
2002 VW Passat V6 30V Station Wagon (SOLD - This car into a money pit)
2011 Kia Sportage "Missus commuter Bus"
2002 Mitsubishi Rosa Bus (converting it to a motor home)

S2rka
Posts: 4
Joined: Wed 18 Jul, 2018 2:56 pm
Model you own: w114
Region: New South Wales
Location: Sydney

Re: W114 rough idle

Post by S2rka » Thu 19 Jul, 2018 9:36 pm

Thanks for the reply Bart!

Car doesn’t have central locking system, but could be ready for it from the factory?

I spent another good 15 mins looking at the brake booster, but can’t see any visible damage.

I see if i got a vacuum meter at work. Stupid question: what should the numbers read if vacuum level is fine?

Cheers,
Henri

User avatar
Bartman4800
300 SLR
Posts: 1985
Joined: Fri 10 Oct, 2008 12:10 am
Model you own: w111
Location: Perth WA

Re: W114 rough idle

Post by Bartman4800 » Fri 20 Jul, 2018 5:29 pm

https://www.onallcylinders.com/2015/05/ ... -problems/

You won't be able to see much on the outside of the brake booster.

It's the rubber diaphragm you need to worry about.

To check whether it is holding vacuum, pull out the hose. If it hisses (air rushing in), it's fine.



Regards, Bart
1963 220 Sb Sedan "Kermit" (Australian Assembly)
1960 220 Sb Sedan "Zum Schlachten" (Early German Assembly, with a torsion bar spring for the bonnet) - Stored in Country WA
1981 Subaru Brumby 1.8 with Weber and 5-speed box "little utie" - Sold to another enthusiast!
2006 Ford Focus "daily driver"
2002 VW Passat V6 30V Station Wagon (SOLD - This car into a money pit)
2011 Kia Sportage "Missus commuter Bus"
2002 Mitsubishi Rosa Bus (converting it to a motor home)

User avatar
TheMadRacoon
C 111
Posts: 853
Joined: Sun 25 Nov, 2012 11:34 am
Model you own: w107
Location: Melbourne

Re: W114 rough idle

Post by TheMadRacoon » Fri 20 Jul, 2018 7:35 pm

Thanks for posting, Bart. Very informative.
Emad,
TheMadRacoon
1975 350SLC Astral Silver (725) / Blue (2012, 284,900 km - present.... a real Benz, getting better and better)
1988 190E Deep Blue (900) / Cream (2006, 190,000 km - 2007, ~ 215,000 km .... FSH and still spent big $$$)
1974 280E Reed Green (860) / Bone (1993, 316,700 km - 2004, ~490,000 km and still A1)

Henry Schuman
E Class
Posts: 53
Joined: Sun 29 Apr, 2018 11:25 pm
Model you own: I own multiple different models
Region: Other (please specify below)
Location: Laguna Park Texas
Contact:

Re: W114 rough idle

Post by Henry Schuman » Sat 21 Jul, 2018 2:18 am

Also you might try these steps if the Vacuum issue is not the problem.
That year I believe had idle solenoids (located at the bottom front of each carburetor and they can go bad causing a rough idle(you can check these by either looking down the throats of the carbs at idle and if bad they will be leaking fuel into the throttle plates and or with the engine off and ign. switched on simply disconnect the wires from them and listen for an audible CLICK ),and they are Fused at # 4 in the Fuse Box I think so be sure and check the fuses!!
Also the Spark Plug connector covers are Notorious for grounding out you can see this on a Scope Pattern or at night you can see them arcing against the cyl head . Both carburetors have Idle air jets beneath the top covers and can be stopped up or restricted .You can Remove the Breather and locate the small holes ,about the size of a ballpoint on a pen then blow air through them to clean out any debris.
Good Luck .
Don't Squat With Your Spurs On !!!!

S2rka
Posts: 4
Joined: Wed 18 Jul, 2018 2:56 pm
Model you own: w114
Region: New South Wales
Location: Sydney

Re: W114 rough idle

Post by S2rka » Sun 26 Aug, 2018 9:24 pm

I really appreciate the help!
I’ve spent a lot of time trying to figure it all out.
So ive listed down everything you guys brought my attention to.
Checked the vacuum with smoke. No leaks anywhere.
It does have solenoids. Checked the fuse no 4 - fine.
Then the wires going into the solenoids. When engine turned off and accessories on, one solenoid is getting power, the other one doesn’t. Ran the blue/pink wire from the solenoid to fuse box and its not there.!? Not sure where’s that second wire (blue/pink) is coming from. So i bridged the other solenoid wiring to the solenoid that wasn’t getting power whilst hoping it makes a positive difference when synchronised. Nothing, still idling the same.
Then tried to pull the wires off the solenoids when accessories on - neither one makes a click.
Next step i tried to close throats on the carburettors when idling, but i couldn’t force them to shut entirely. They stay open about 20mm. Not sure if stuck solenoids keep them open. Could it be?
Still idling very rough.
Lastly i sent some compressed air through the air jets etc.
Tried to start it - voila, idling perfectly.
So i drove her around town with a big smile on my face for half an hour. Parked for 1.5hours and went for another drive and started idling just little rough every few seconds, like skipping a beat.
Went for a drive this afternoon to see if i can detect any kind of pattern in the behaviour. At first it took a few gos to get her running, but idling seemed fine. Everything normal when driving and when stopped at traffic lights i could feel just a little or no issues with idling.
After driving for about 20 minutes it started to idle a bit rough when stopped again. And it was getting a little worse in time, but idled a little better when not in gear.
Sorry for the novel guys.

Henry Schuman
E Class
Posts: 53
Joined: Sun 29 Apr, 2018 11:25 pm
Model you own: I own multiple different models
Region: Other (please specify below)
Location: Laguna Park Texas
Contact:

Re: W114 rough idle

Post by Henry Schuman » Sun 26 Aug, 2018 11:38 pm

If you blew air through the Idle jets and it idled perfect then do it again .
The fact that the solenoids are not clicking is bothersome to me as IF they are NOT actuated at IDLE fuel will be gurgling out in the carbs thru drowning the engine in overfueling at idle >
SO clean the idle jets again see how it idles then with the ENGINE RUNNING ,breather off peer down the throats of the carbs and see if you see fuel trickling down the throats at idle.
One other thing is you said you had the ignition in the accessory position and you need to have it in the RUN position to check those solenoids.
I do NOT advise patching one wire to another for several reasons and it makes no sense that you had one clicking then now you have none ???
Don't Squat With Your Spurs On !!!!

S2rka
Posts: 4
Joined: Wed 18 Jul, 2018 2:56 pm
Model you own: w114
Region: New South Wales
Location: Sydney

Re: W114 rough idle

Post by S2rka » Mon 27 Aug, 2018 9:24 am

Thanks Henry!
Neither of the solenoids were clicking, just one of the wires running into the solenoids had power in it.
I only patched the wires to see if it made any difference, didn’t leave it this way.

mathuisella
560 SEL
Posts: 596
Joined: Sun 08 Jun, 2014 6:03 am
Model you own: w123
Location: Brisbane, North side.

Re: W114 rough idle

Post by mathuisella » Sat 03 Nov, 2018 1:37 am

Just a quick thing... check your engine mounts... even if they look good, they are probably worn, cheap fix and so worth it.

Post Reply

Return to “W114 and W115”