Regeneration Valve - is this the cure for my rough idle?

[IMD]

It seems that I'm not the only person who has experienced a very rough idle problem with my W124. I've recently bought a 1993 e220 estate. In Drive or Reverse, the revs fluctuate between 500 and 750, sometimes quite eratically, almost feeling like the thing is going to stall, other times not at all. In Neutral or Park, the revs raise to about 750 and stay pretty steady.

I took the car into an independant Mercedes specialist today and he ran a full diagnosis with the ECU, as well as spending a couple of hours checking over the car.

He has found that the regeneration valve is not working and this, he thinks, could be the problem, rather than the MAS. When he initially disconnected the vacuum lines from this valve unit, and played around covering and uncovering the tubes, the revs fluctuated in the same way. His suggestion is to replace this and see if it cures the problem.

I'll let you know what the outcome is later next week, after he has done the work. £75.00 including fitting seems cheaper than a new MAS!

 

[Dieselman]

The fault does sound like an intermittent air leak so that would suit.

You could try blocking off the valve to manifold connection and see if it runs better or worse..

 

[television]

Rough Idle can be many things. Do you know what system your car has

 

[IMD]

Hi Malcolm

Excuse my ignorance, but what do you mean by 'system'?

 

[KLP 92]

I would buy a MAS from ebay first. Its the most common fault on them.

 

[Glenn Smith]

I would buy a MAS from ebay first. Its the most common fault on them.

I wouldn't buy anything off of Ebay!

Just guessing but by regeneration valve do we mean exhaust gas recirculation valve? if so it is a good idea to blank this off to eliminate this first, often people don't bother replacing just leave blanked. too much egr will cause poor running especially at idle and lower speeds when only very small amounts can be tolerated before drivability is seriously affected.
To blank it off you need to either blank the pipe where it comes off the exhaust or where it goes into the manifold, no goo just blanking the vacuum control pipes as this will not stop exhaust gasses leaking by into the inlet manifold.

 

[television]

I wouldn't buy anything off of Ebay!

Just guessing but by regeneration valve do we mean exhaust gas recirculation valve? if so it is a good idea to blank this off to eliminate this first, often people don't bother replacing just leave blanked. too much egr will cause poor running especially at idle and lower speeds when only very small amounts can be tolerated before drivability is seriously affected.
To blank it off you need to either blank the pipe where it comes off the exhaust or where it goes into the manifold, no goo just blanking the vacuum control pipes as this will not stop exhaust gasses leaking by into the inlet manifold.

If you can blow down the pipe coming from it, then it is stuck open

 

[television]

Hi Malcolm

Excuse my ignorance, but what do you mean by 'system'?

Injection / ignition sytem

 

[kth286]

It will be the electronic engine with two coils feeding 4 cylinders.

I think he is taking about the closed loop petrol vapour system which has a little pulsating valve on the inside wing NS.

Could be a clogged charcoal filter or lambda probe up the shoot.

The coolant sensor is also critical.

I am not sure it has the MAS in the induction tract as per later models.