D40 rough idle

[acko13]

OK folks, I need help with this one.
My 2010 Spanish built D40 has 140,000km and had been running beautifully.
Came home from a 300km in the country, parked the car, but when I went out put it away a hour later it was idling very roughly, sort of like a four cylinder car on three pots.
A drive around did not clear the problem. Next morning when cold it sounded like a chaff cutter. but seemed to improve when warmed up.
It was showing signs of it being the injectors and having heard horror stories of people being charged up to $8000 for a replacement, I took the car to a diesel specialist rather than my Nissan Dealer. The vehicle has always been dealer serviced before.
He plugged the diagnostic tool in and sure enough number one was not firing and number three was suss.
OK, full replacement of injectors (just under $3000) and I was told all was well.
Got the car back and not so good. After a couple of days it was a bad as ever. Funny thing is that it still goes beautifully running along the road, but the idle is a shocker, and the exhaust smells like raw diesel coming out.
In fact everything but the idle is OK. Runs well at highway speed and pulls like a train.
Any suggestions, before I take it back to the specialist?

 

[Old.Tony]

Suction control valve would have been my first thought. Try a bottle of injector cleaner in the tank and drive it for 100km or so, or go for a faster solution and do a diesel purge (Liqui Moly Diesel Purge). If that does fix it, the SCV was dirty and is suspect and may fail at some point in the future (we've all been there).

Other possibilities: EGR valve is sticking open a little allowing exhaust gas in at idle (it's not supposed to). The 2011car did not have flow sensors, so you could just put a blanking plate (1mm stainless steel copy of the gasket on the EGR valve end of the EGR tube but don't copy the big hole).

Unlikely to be a turbocharger failure if it's still pulling well, and the turbo doesn't boost at idle anyway, but air still has to flow through the intercooler so that needs to be clean (have you cleaned it, and do you have a catch can?).

A dirty MAFS might also cause some issues but usually more with higher power levels. If you've got some electrical contact cleaner handy, remove the MAFS from the air intake just outside the air filter, spray the cleaner in the little hole in the end, do NOT put anything in there or it will break ($400!) and reinstall.

Hope it's one of those!

 

[acko13]

Suction control valve would have been my first thought. Try a bottle of injector cleaner in the tank and drive it for 100km or so, or go for a faster solution and do a diesel purge (Liqui Moly Diesel Purge). If that does fix it, the SCV was dirty and is suspect and may fail at some point in the future (we've all been there).

Other possibilities: EGR valve is sticking open a little allowing exhaust gas in at idle (it's not supposed to). The 2011car did not have flow sensors, so you could just put a blanking plate (1mm stainless steel copy of the gasket on the EGR valve end of the EGR tube but don't copy the big hole).

Unlikely to be a turbocharger failure if it's still pulling well, and the turbo doesn't boost at idle anyway, but air still has to flow through the intercooler so that needs to be clean (have you cleaned it, and do you have a catch can?).

A dirty MAFS might also cause some issues but usually more with higher power levels. If you've got some electrical contact cleaner handy, remove the MAFS from the air intake just outside the air filter, spray the cleaner in the little hole in the end, do NOT put anything in there or it will break ($400!) and reinstall.

Hope it's one of those!

Thanks mate, I will chase those up with my mechanic.

 

[Tappet]

still goes beautifully running along the road, but the idle is a shocker,

Got all the hallmarks of a crook Suction Control Valve. As old Tony for mentioned try some Liqui Molly Fuel system cleaner, there is other brands such as Nulon. While you at it change the fuel filter. In Fact I would probably do that first. Do a fuel pump/ecu reset and let it idle for 15 minutes. Do inexpensive easy tricks first.