W210 E430 ECU disconnected, rough idle

[perbilse]

Hi,

newbie of sorts here. I've looked all over, but can't find a solid answer. I've had the dreaded ABS/BAS/ESP problem, and replaced the brake switch to no avail. I then came across several suggestions that the fan in the ECU box (behind the brake hydraulic control block) might be broken or stuck, so I decided to haul out the ECUs to look for a fan. There is what looks like a fan at the bottom of the box, but it's more of a weekend job to get at it so I put the ECUs back.

Upon starting, idle is extremely rough, and the engine is hunting and vibrates badly when gear is engaged. It seems to improve a little over time, and seems to disappear at higher revs in neutral. I realise disconnecting the engine management ECU might cause it to lose adaptation data, but how long should I expect it takes to re-learn? And is there a procedure to follow, or can I just drive off? I've double-checked cables and connectors, and everything looks fine on that front, and there are no warning lights or other indications of a fault.

Thanks,

-- Per

 

[johnsco]

A common cause of the ABS/BAS/ESP problem on these cars is corrosion around the earthing point behind the right-hand (off-side in the UK) headlight.
This has happened to me.
This earth stud has about 15 brown wires going to it.
The metal around these earth points corrodes badly and the stud can sometimes detach from the panel.
My solution was to gather all the wires into one crimped sleeve and take a heavy copper earth wire to a stud near the accelerator potentiometer.
That cured it.

Another common fault on these cars is a break in the ABS sensor ring on the rear wheels.
Again - The fault lights are the same.

 

[perbilse]

Johnsco, many thanks for your note. I'll definitely look for the earthing stud you mention; I had already checked the stud close to the brake hydraulics block with three or four wires going to it, I thought that was the one for the ECUs. Interestingly, the problem only manifests itself in hot (London) weather; August to May it's very rare to see it, but queueing on a hot day in July is almost certain to bring it on.

In the meantime, it would be great to hear if anybody has any experience with ECU re-learning. Looking at posts for other makes, it seems to be a case of idling for 5-10-15 minutes, stopping and starting the engine once or twice (while hot), and driving for up to 100 miles, but are there any particular Mercedes quirks and gotchas? These aren't exactly unknown to exist.

Thanks again.

Best,

-- Per