2007 Renault Megane Scenic 1.9 dci rough idle & smoke

[Conanius]

Hi All,

My brother in law has a Renault Megan Scenic Diesel with a bit of an odd fault.

Intermittently, irrespective of hot or cold engine, he's got a really lumpy idle that increases with engine speed up to about 2000 rpm and then vanishes and immediately returns. When its doing this lumpy idle, a noticeable amount of black smoke is trickling out of the exhaust - it isn't huge clouds.

We've checked for fault codes and there aren't any shown. It apparently started about the same time that the airflow sensor was replaced. It's also recently had new air filter, glow plugs and fuel filter.

We're going to take a peek at the air flow sensor and see whats going on there - maybe a loose/dirty connection? - but any ideas what it might be/other things worth checking?

 

[Brookert]

Was it a genuine maf?

 

[Orionaut]

Hi All,

My brother in law has a Renault Megan Scenic Diesel with a bit of an odd fault.

Intermittently, irrespective of hot or cold engine, he's got a really lumpy idle that increases with engine speed up to about 2000 rpm and then vanishes and immediately returns. When its doing this lumpy idle, a noticeable amount of black smoke is trickling out of the exhaust - it isn't huge clouds.

We've checked for fault codes and there aren't any shown. It apparently started about the same time that the airflow sensor was replaced. It's also recently had new air filter, glow plugs and fuel filter.

We're going to take a peek at the air flow sensor and see whats going on there - maybe a loose/dirty connection? - but any ideas what it might be/other things worth checking?

The big problem with these is usually the EGR valve getting totally clogged up. But I cant remember this ever causing engines to run off all on their own.

If you do remove the EGR, be VERY careful not to let any of the gunge/grit fall into the inlet manifold. It can get onto the valve seats when you next crank the engine and while it will not do any damage as such it can stop the valves from seating properly meaning that the engine can become very difficult to start due to poor compressions (Once the engine is started this will clear, but starting can be a problem)