W108 3.5v8 warm running problem

Helloi live in New Zealand and have a 72 280se 3.5it starts well when cold but after ten minutes when warmer it will stall and won’t start. Leave it an hour and it will then start again and stall. When cold the engine will start and runwhen cold the engine will surge up and down in park .reading your forum it seems the surging may be a faulty AAV? Is a faulty MAP causing the warm running and starting issues?thanks in advance for your help kind regardshemal

Hi Unknown,

would be great if you could sign with your first name so that we can address you as a friend here.

Surging to 2000 rpm and then dropping to 500 rpm repeatedly is normally an issue of false air and mostly caused by broken AAV.

Ten minutes is a long time before you car stalls. Did you verify fuel pressure and whether you loose fuel on hoses or injectors? Then please have a look at your spark plugs. Are they black or brown or white? Does your exhaust smell oil or fuel when engine is warm?

Please check whether MAP sensor holds vacuum. There is a video in my compendium how to check.

New Zealand was my favorite holidays in 1996. My god what a long time ago. Always green and nice temperatures.

Hello,

Many thanks for your prompt reply. Maybe it is closer to five min when it stalls and so I suspect it relates to the increased engine temperature. I managed to keep driving by keeping the car moving. If the car came to traffic lights then it would stall. And not start until after 60min…

I will try and check the plugs and MAP functioning. Does this sound like a case of MAP failure allowing too much air to the system and the ecu compensating inappropriately and then flooding the engine? Oil has a slightly petroleum smell.

I am pleased you enjoyed your time here in ‘96.

Kind regards,

Hemal

Hi Hemal,

it was marvelous in NZ. I went through both parts in a car and stayed in B&B .

For your car it would be typical that MAP sensor does not hold vacuum and signals high load to ECU which sends too much fuel, especially in idle. Petrol in oil speaks for that. But that is only 1 possible cause. Also check leaking injectors, leaking cold start valve, wrong reisistance of engine temp sensor on ECU connector.

Cool, actually we are in NZ, Vrouwenpolder, Minicamping. 
Is the problem that he gets to much or to less fuel?

Greetings from Minicamping, Martin 

A leaking MAP sensor creates too much fuel in idle and part load.

I understand, that’s why he runs cold better than warm.
Thanks

Hello Dr,

A small update. I occluded the AAV with a small plug with a hole drilled through it. My hunting idle is now solved and it doesn’t get so cold here so I think this is ok. Again today the car stalled when at traffic lights after ten min of driving and wouldn’t start. I also noted it turning over rather slowly at this time. Two hours later it starts ok and I drive home. Could it be bad voltage regulator, battery or alternator causing this condition. I thought if MAP sensor then it should still turn over quickly? Btw MAP I have checked and resistances are ok and hose looks good. Haven’t done vacuum test as don’t have this tester. Thanks again,

Kind regards

Hemal

Hi Hemal,

I can confirm that D-Jetronic runs badly if your voltage drops too much.

you have to check vacuum leak of MAP sensor. Resistance is not enough. And I will not comment on your AAV closing . I also do not understand why you left a hole in it. It closes completely on hot engine when it works properly. Unless you live at 80°C environmental temperature an AAV still has work to do from 20° to 80°C engine temp.

Hi Volker,

Many thanks for your prompt reply. I will find a vacuum tester and check the MPS as per your guide.

Very frustrating to have to push the S class across an intersection!

Alternator tested ok so I am not sure why it wasn’t spinning over well after stalling…

Hi Volker

I hope you are well. I can confirm that the MAP sensor holds 15in of hg for more than 10 seconds. Where do you think I should go to next?

Kind regards

Hemal

Hi Hemal,

are you able to measure exhaust gases. Especially CO and HC ?

Hello Volker

I will try but not sure I have a way of doing this

Is there a way of finding out by looking or smelling?

Thanks

Hemal

Hi Hemal,

that depends on the quality of your nose.