E320 Surging/Hunting

[Julianshaw]

I've had my automatic 1996 E320 cab for a few months now (lovely car) but lately it has started to try and go when it shouldn't! When stopped and still in drive with the footbrake on it surges with the revs oscillating between 300 and 900 rpm every couple of seconds. Put it into neutral and it quiets down properly. I left it in the shop for a day and it stopped doing it after a while and they found nothing and said nothing was wrong but charged me £70. But it nearl;y always does it. Anyone got an idea?

 

[kid-jensen]

Intermittent problems like this are always a pig to track down.
300 rpm is way too low, the engine management will think it's going to stall and will try to correct the speed, hence the surging.
Start with the cheap stuff! The idle speed controller has a hard life and can get gummed-up with carbon. They usually respond well to a good clean. Comma Carburetter cleaner works a treat, dessolving carbon deposits in a few squirts. You may even get away with cleaning it in situ, but removing the thing to check if it's sticking is advisable. After that it's probably time to spend some money........

 

[jmcbuilder]

Hi I had the same thing had my oxi sensor changed & my air flow thing changed i dont know the proper names. Not cheap but it worked. Andy will know what i mean.

:lol: Jamie

 

[Andy]

Hi all

You mean IDLE ACTUATOR & OXYGEN SENSOR. I think Paul G is on the right track. Try cleaning before getting really involved. It sometimes work.


Regards

Andy @ www.mercedesservicing.com

 

[Julianshaw]

Thanks for you help

Thanks for your help so far everybody. I'll keep you posted.

 

[Julianshaw]

The problem is solved. :lol: The correct name (from Mercedes) is a "Regeneration Valve" costing £54(!) plus testing and fitting £30(!!). Another description is the "Evaporator Cannister Purge Valve".

 

[piestore]

hunting in drive

Trickey one

Test brake servo for leaks or just dissconect servo vac pipe block up pipe to engine and test drive SLOWLEY brakes will be VERY heavy.

Air mass metre possible

or gearbox lockup clutch, does it try to drive away at tickover?