Erratic rpm when cold

[saskak]

Hi All,

I have a slight issue with a bit of erratic rpm when cold. It is a M59, 2007, 1.6hdi (9HXC), no FAP, 80k miles.
When the car is cold and I am rolling to a stop (brake pedal pressed), the rpm drop to ~700 or so, almost stalling and then once stopped they return to normal (~800-850-900). Once the engine has warmed, there are no such issues. When cold the idle rpm are stable without any issues, only when just about to stop.
There are no errors and everything looks normal. Battery is on the older side, ~5-years old, but starting has been faultless and battery connection is the clamp-type. I have not measured the battery output, but it has not missed a beat.

Is this normal, or there might be something going on. I am not too sure, but it seems like the now slightly colder weather exacerbates the rpm thing.

Cheers,
saskak

[polar]

The 1.6hdi can be a bit erratic with the idle rpm when cold, it may be exasperated if you have a couple of glow plugs down.

If its okay when warm and does not stall when cold i would not worry too much although you could get a diag done for piece of mind.

[saskak]

The 1.6hdi can be a bit erratic with the idle rpm when cold, it may be exasperated if you have a couple of glow plugs down.

If its okay when warm and does not stall when cold i would not worry too much although you could get a diag done for piece of mind.

Thanks polar.
I have a cheap Chinese DiagBox/Lexia and this reports no faults. I have replaced all the glow plugs ~2 years ago, but will probably test them again.
Good to know that it was not just me.

[Trevor]

This is groping in the dark but have you pressed the brake pedal when the engine is cold to see if the revs drop? I wonder if the problem is something vacuum related

[saskak]

This is groping in the dark but have you pressed the brake pedal when the engine is cold to see if the revs drop? I wonder if the problem is something vacuum related

Hi Trevor,
No it does not do that. Only when it is rolling to a stop and then in the moment of stopping or just before that goes down and then stabilizes to normal. I would say it may be somehow linked to the speed sensor somehow.

Cheers,
saskak

[ffrenchie]

This is groping in the dark but have you pressed the brake pedal when the engine is cold to see if the revs drop? I wonder if the problem is something vacuum related

Vacuum is generated by a pump not taken from the inlet like a petrol isn't it ? Throttle position sensor or MAF might be worth a look and try some injector cleaner in the fuel.

[saskak]

Vacuum is generated by a pump not taken from the inlet like a petrol isn't it ? Throttle position sensor or MAF might be worth a look and try some injector cleaner in the fuel.

I will certainly try the injector cleaner in the fuel. Would not a MAF problem result in some sort of an error. I can certainly unplug it and see if there is a problem, but I would have thought that there has to be an error.

cheers

[polar]

Vacuum is generated by a pump not taken from the inlet like a petrol isn't it ? Throttle position sensor or MAF might be worth a look and try some injector cleaner in the fuel.

I will certainly try the injector cleaner in the fuel. Would not a MAF problem result in some sort of an error. I can certainly unplug it and see if there is a problem, but I would have thought that there has to be an error.

cheers

MAF does not usually through a error code.

[ffrenchie]

Vacuum is generated by a pump not taken from the inlet like a petrol isn't it ? Throttle position sensor or MAF might be worth a look and try some injector cleaner in the fuel.

I will certainly try the injector cleaner in the fuel. Would not a MAF problem result in some sort of an error. I can certainly unplug it and see if there is a problem, but I would have thought that there has to be an error.

cheers

MAF does not usually through a error code.

I had a MAF problem with no code and it ran better disconnected. It still didn't throw a code up either. A new sensor cost me about £40.

[saskak]

I might as well replace it and see if this makes a difference.