Hi,

 

new to diesels so please excuse me if this has been asked before. What should the idle Revs be normally ? It’s a 67 plate 2.0 SE L. Notices that the revs are usually sitting at the 1000 Rpm mark, then drop to 800 once warmed up. Is the 1000 Rpm a re-gen or to do with cold start ? Only once have the fans kept running when the car is off which I assume is a regen ?

 

cheers

Regen's happen roughly every tank-full of fuel.  High-idling at 1000 rpm (accompnied by fans and a burning smell from the car) means regen is happening.  Falling back to 780-800rpm means standard idle.  Unlike the TSI engines, TDI engines (Euro 6) don't generally utilise higher revs at cold - they might initially sound lumpy for the first minute whilst the ECU regulates the fuel/air mix to get the car warm.

It is recommended you let the car continue when it does its regen; a fast blast (2800rpm at a constant 20 or so miles will give you a nice clean DPF)....just drive normally, but one gear lower.

I have the same year and model car and can confirm that my vehicle actually revs higher on cold mornings until about the same time as the engine reaches operating temperature. It may not do it for a few minutes after first starting the vehicle and it can easily be mistaken for a regen. I personally think it's just the load on the alternator as it's recharging the battery from overnight and getting the heaters to warm up the inside of the car. How I can tell it's not a regen is that the rev counter is slightly higher than that of the regen's. My mate's 16 plate 1.6 estate also displays the same behaviour. 

Cold temperatures will keep the engine idle speed slightly higher. Coming home the past few nights it's been around 0-4'c and the car's idle has been similar to the OP. I've had the blowers on high initially just to get a bit of warmth into the cabin (heated windscreen on Tuesday with there being a smidge of ice about), but not for too long. At the end of the journey I've stopped at the lights and it hasn't wanted to stop start, even with the engine at full temp. I know it's not been doing an active regen because it doesn't smell like a tyre fire when I'm taking my gear out the boot. I'd assume it's just a case of the electrical consumption is high (climate control, heated seat, headlights) and the cooler temperature.

 

Passive regens would (and should) be happening all the time if the exhaust temperatures are high enough. I wouldn't have thought a marker such as a tank of fuel mileage for a regen to start is the case. It'd be more a case of the soot quantity in the DPF reaches the threshold (25g IIRC) and then the active regen kicks in until it's dropped below the 'turn off' threshold.

Edited 4 March, 20215 yr by tunedude