Rough engine

[alan695]

i need your help!!
I own a 1997 R170 slk 230, i have a major engine problem
I have no warning lights..
Engine will fire but runs so rough then cuts out..
If i start her and give it some revs it will rev up but there is a smell of unburnt petrol, if you take your foot off the accelarator it will return to rough running them cut out again...
I have some skills on engines but have no idea where to start. Can you great people help..

 

[Flackadder]

Is there a spark where there should be? That would be my first port of call. Too much air...to little. if you are standing over the engine there are many things that should have your attention.

As someone with 'some skill'.

Basics first.

 

[Bellow]

Over fuelling or under igniting.
More likely the former as ignition problems are usually on the HT side and will cause the miss-fires to occur on opening the throttle. Could still be ignition related LT side but I'd explore the fuelling first.
Someone will know any weak points of your model, but for now I'd check the fuel pressure regulation on the basis that all cylinders appear to be affected. Are all the pipes to the fuel pressure regulator present and correct?

 

[Martin Theron]

Sounds like "false air" taken into your intake manifold. Usually there are a few air pipes connected to your intake system after the throttle body. If one of these leaks air then your air/fuel ratio will be incorrect since the leaked air is not measured by your air mass meter. Under idling conditions this is at its worst causing rough idling and cutout. Good luck.