Starship

My W124 300E has occassionally been stalling at low speed or idle. The starter is fine and turns-over ok but she refuses to start for about 5 minutes until cooled down a little.

bjay51d

I would check the oxygen sensor...And the ovp relay.

I was having the same problem until I canged out these two components

YNVDIZW124

check the EHA next to the fuel distributor and the OVP relay..The oxygen sensor you should change with one from a 1990 mustang with manual transmission...

doc willy

i had the same problem this week with idle going down to 300rpm then stalls

clean the ICV but to no avail
another possibility is the engine coolant temp sensor 4 pin plug on my benz 300-24v although i think it seldoms fails

this is what i have learned and discovered: tweaking the EHA

remove the 2 screws (flower hex) of the EHA, be careful with the 2 O rings

when removed, you would see a gold screw, unwind it CCW about 10 turns to remove, then remove the flat washer (this screw serves as the seal to EHA
adjustment)

get a 2 mm regular hex wrench insert carefully and adjust 1/4 turn CW then resinstall the washer and screw

resinstall the EHA back to fuel distibutor and test drive.
if still idles low and stall, repeat EHA adjustment with another 1/4 turn CW

you will feel the increase response on acceleration and increase rpm at idle

this is actually the main idle adjustment while the AF ratio is the secondary
idle adjustment (only when AF adjustment fails that you tweak the EHA)

my stalling improved after 2 adjustments of EHA(total of 1/2 turn CW)

although manual says idle cannot be adjusted, wear and tear makes the EHA go lean through the years. For workshop job, they calibrate the chamber pressures but for DIY i think you could give this a try (seen article this in shopforum: search EHA adjust on title)

Starship

Thanks but I think it was the OVP which I replaced.

NorCal124

Sometimes you don't need to replace the entire OVP relay, just the 10 amp fuse inside it.

shadowgriffen

I think thats what everyone means when they say OVP...

to this day I've yet to hear about someone replacing their entire OVP relay.

Bigpete123

Interesting. The guys on mercedesshop recommend replacing the entire relay all the time. In fact, what I read is that your OVP relay often goes bad even when the fuse is intact. Oh well.

I actually replaced mine. The previous one didn't have a blown fuse. However, it turned out that the OVP relay didnt' fix my problem, so I probably just replaced a good relay. Oh well!

Regarding the EHA adjustment, I have seen that recommendation a lot. It just seems to me that it's a bandaid though... kind of a last-ditch effort. In other words, why would the car develop these problems in the first place? It doesn't seem like all of a sudden an adjustment would be needed out of the blue unless something was failing.

My mechanic has adjusted my EHA on a number of occasions. It fixes the problem for around 200 or 300 miles, then problems come right back.

Anyway, other culprits just based on my research (not experience) are:

OVP relay
02 Sensor
Fuel Pump Relay (or MAS control unit, depending on your car)
Plugs,wires, cap
Idle Control Valve

Good luck. I have had a similar problem haunt me for over a year now.

Koolwipski

I was told by a mechanic that this problem usually occures when the Throttle Control Valve goes bad (I hear this will happen sometime after after 100k miles).
This is on a 1992 400E. Then, as a follow up to that comment - I was told that if i had not replaced my upper wiring harness - to do that first.
Just passing along the info.
Steve

bjay51d

After I fixed the stalling problem.I started gettin a wandering idle so I yanked out the ICV and installed a plumber valve.with doing this I can totally control my Idle speed.

doc willy

an inexpensive suspect for hunting idle are the fuel injector o rings

low idle is common problem in 124 as mentioned in stu ritter book
and tweaking the eha to give a lower chamber pressure to o.45 bar instead of the factory settingof 0.40 to compensate for wear and tear including air leaks (i suggest it as a last resort after checking other causes mentioned)
you could give it a try and its easy to reverse if it fails.

my e300 24 valve now runs livelier with growl with no stalling, easy start now less than 3 secs and less lag and hesitation
much better than the last 4 years

shadowgriffen

Platinum Plugs can cause erratic idle.

If any of you have platinum plugs replace immediately for super coppers.

FYI

doc willy

bad ect