W126 300SEL cutting out on tick-over

[gazzoouk]

Hi,
i have been searching the posts to identify anyone that has found a solution to the same problem that i am experiencing on my 1988 300SEL. I have found a load of posts but i would appreciate an "idiots guide" to checking and testing for the problem as at the moment i'm clueless.

I am getting an imtermitant problem with the car cutting out. The car starts first time everytime in the morning and runs perfectly the problem appears to occur there after when it has been driven (although no doubt it will prove me wrong today!).
I turn the key the engine fires up but then cuts out. If i keep my foot on the accelerator it is fine but as soon as i release it it dies. Usually after holding the revs at about 1500rpm and slowly releasing the accelerator the engine stabilises at 500-750 rpm. But this can take up to 8 attempts.

I have read threads that indicate similar problems and some of the culprits could suggested are;

Over voltage resistor, MAF?, Idle sensor, ECU, Idle valve, throttle body?????


I would really appreciate some help. Also can anyone let me know if my car is fuel injected or has a carb?

best regards

Gary

 

[Telegraph-Hill]

300 S E L means... S=S-class E=injected (einspritzung) L=Long version. 300=3L Engine called M103. 300SEL=Great car

Greez,
Oli
who can test and check the system only on the car itself.. :-(

 

[gazzoouk]

Another observation

Thnx Oli,

further to my post i forgot to mention that at tick-over the revs keep rising and falling.

Please, can someone offer a suggestion?

Gary

 

[television]

This sounds very much like an air leak around the inlet minifolds some where,,check the plastic pipes on the vacuum system for spits etc

http://www.detali.ru/cat/oem_mb2.as...&L=765.706&CT=F&cat=568&SID=80&SGR=015&SGN=01

 

[television]

Also all of the pipes and vaccuum parts in the link

http://www.detali.ru/cat/oem_mb1.as...9351&GM=717.431&L=765.706&CT=M&Cat=505&SID=14

 

[gazzoouk]

Malcolm
thank you for the response. I hope it is as simple as a split in the plastic pipes.
I will check them, it's a bit cold to do it at the moment .
Gary

 

[television]

we do get a lot of unsolved post like yours I would go to the point of buying some new piping and changing all that you can see,,it is now 20 years old

Cheap from indoor fish shops

 

[kenwood]

Idle Cutout

Hi, I had a similar problem on my 300CE .Started first time but after a journey would be erratic in idle. Tried all the usual fixes , my indie sorted it. The problem was the air slide valve on the fuel metering head. Hope this helps, Kenwood.

 

[Telegraph-Hill]

Thnx Oli,

further to my post i forgot to mention that at tick-over the revs keep rising and falling.

Gary

there is a Poti In the air flow sensor housing. They are getting old. You need to check the resistance with a (analog)meter by pressing down the air intake you see underneath the air filter housing. If there is a steady change without jumping to different readings the Poti is OK. Otherwise it needs to be changed and the system needs to be set up. This is usually nothing you can do by yourself. Before you start checking the whole system you may need to measure the fuel pressure first to be sure you are not chasing a phantom. We hear about many people changing it by them self and having problems the car starting after it in the German W124 forum. Everything else like old hoses etc can be checked of course. I have some experiences with a hand full of M103 engines over the last 5 years and I found a lot of possible problems with the old KE Jetronic system. A dirty oxygen sensor if Cat is fitted is also one of those.

Greez,
Oli

 

[television]

If the car has to go in for repair Bosch service centers are much cheaper than MB

 

[jaymanek]

idle speed control valve and pipes around there is the first place to check...

 

[gazzoouk]

idle speed control valve

Hi Jaymanek,

firstly thanks for the reply. Can you please tell me where i would find the idle speed control valve and what i am checking for?

thank you

Gary

 

[television]

Its to the right of item 5 in the link, thats if you have the rotary idle valve

Connecting 12 volt over the terminals it should buzz

http://www.detali.ru/cat/oem_mb2.as...&L=765.706&CT=M&cat=505&SID=07&SGR=015&SGN=01

 

[gazzoouk]

More help please

Thanks Jay/Television and all,

i have taken the idle control valve off and put 12V to it and i can see it opening and closing (it makes a single click as it opens then closes) as i apply then remove the voltage source. I cleaned the contacts and replaced the valve. I assume this means that it is working? Also checked that i was getting 12V at the contacts when re-connected - all OK.

i have also checked the OVP relay fuse (it has a single 10A) and it is not blown but i'm not quite sure how to check if the relay is working?

I checked the pipework as far as possible and all seems fine and no splits.

I have just been for a run in the car and it is still doing the exact same thing.

Can anyone suggest the next item to check.

This problem is driving me nuts.

I really appreciate you taking time out to help.

very best regards

Gary

 

[gazzoouk]

Update

Still having the same problem.
I have checked the following;

1. I checked the pipework as far as possible and all seems fine and no splits.

2. I removed the idle speed control valve and put a 12V source across it and i can see it opening and closing so i assume this unit is working. I replaced the valve and checked with a meter that i was actually getting a 12V supply to the valve from the loom and all is well.

3. I have also checked the OVP relay fuse (it has a single 10A) and it is not blown but i'm not quite sure how to check if the relay is working? I ordered a second hand unit which i fitted but now the ABS light stays on and the car won't rev. I guess this replacement unit is genuinly faulty.
Can the OVP relay be faulty even if the ABS light doesn't come on ?

I have put the old OVP relay back in and now the ABS light goes out as it should, the car revs but still will not consistantly tick-over.

Please please help.

This problem is driving me absolutely mad.

regards

Gary

 

[jaymanek]

there is also an idle speed relay under the dash, an absolute pig to get at... could also be the culprit, you need to see if the idle valve is getting 12V across it or not..

 

[gazzoouk]

Problem Solved and a big thank you

I believe my problem has been solved. I say that with my fingers crossed as i have only test driven it 5 miles with about a dozen stop-starts.

I fitted a second hand OVP relay only to find that the ABS light stayed on and the car still did not tick over.
I thought well nothing to loose so i took the tin can off the relay (the one i had purchased as a replacement but was making the ABS light stay on) to expose the innner workings. I had read that some of these relays suffered from dry joints. So i got myself a cheap (£5) soldering iron and a bit of solder and went around each solder joint on the PCB (only about a dozen in total) and heated them up in turn and applied a little more solder.
The whole job only took half an hour. Popped the relay back in the car and Bob's yer uncle, Fannies yer Aunt it works. Lovely smooth tick-over and it doesn't cut out at junctions.

What a pleasure

A real big thank you to everyone that took the time to give me pointers on how to solve the problem.

My faith in humanity has been restored by the amount of people willing to offer advice, even people in the trade through this forum.

So thanks again and long may this forum last.

I'm going for a couple of cheeky wet ones.

Gary:smile::smile::smile::smile::smile: