2010 C350 Sport “auto-choke” problem

[KolC350MXB]

I have an “intermittent” fault that when the car is fully warmed up, the “choke” for no reason, will switch back on again. Stopping the car and switching off the ignition and then restarting, initially stops it, but it will then come back on a little while later (which is especially frustrating in stop/start traffic).

There seems no pattern to this fault. A long run (after a number of small trips around town) seems to clear it, but conversely after giving the car a bit of “welly” when already hot, seems to switch the ECU controlled “choke” back on. Any thoughts please? Thanks, Col.

 

[supernoodle]

The last time I saw a choke was on my mum's mini metro.
As you have a diesel, what are referring to by choke? Or maybe just describe the symptoms you experience.

 

[LostKiwi]

I'm thinking that what you're describing us a regen. Do you have a DPF on your vehicle?

 

[mioba]

How do you think its the choke, last time I seen a choke on a car was...I dont remeber, but many on garden machines. I havent seen a choke on a merc not even from my first a W124.

I am not even sure mercs have choke lights.....have you had the car scanned for errors by a decent merc indy, thats the first thing you need to do.

 

[KolC350MXB]

I'm thinking that what you're describing us a regen. Do you have a DPF on your vehicle?

Hi. Yes, I have DPF on my car.

 

[KolC350MXB]

How do you think its the choke, last time I seen a choke on a car was...I dont remeber, but many on garden machines. I havent seen a choke on a merc not even from my first a W124.

I am not even sure mercs have choke lights.....have you had the car scanned for errors by a decent merc indy, thats the first thing you need to do.

Hi. (Yes, and no errors detected). When I start my car from cold, it “fast idles” for the first 4-5 minutes, at around 750 rpm. It then suddenly drops, to it’s normal idle of around 550 rpm and normally stays there. (At 58, this reminds me of the equivalent actions of an automatic choke on carburettors in the 70’s/80’s).
I have DPF on my car, and someone has suggested since posting, that at times, it is trying to “burn off” from a sensor the diesel particles on the sensor/filter by running at higher revs. If so, this sounds like I need to replace a sensor, the DPF itself or worse, the ECU?

 

[LostKiwi]

As I said idle rpm rising is normal behaviour during a regen. There will also likely be additional heat generated and the exhaust note may change and there may be differences in the way the vehicle exhaust smells.

All normal.

Elevated idle when cold is similarly normal as it assists the warm up process of the engine.

 

[star]

As above and if the car deems the battery is low, it will increase the idle.

 

[KolC350MXB]

As I said idle rpm rising is normal behaviour during a regen. There will also likely be additional heat generated and the exhaust note may change and there may be differences in the way the vehicle exhaust smells.

All normal.

Elevated idle when cold is similarly normal as it assists the warm up process of the engine.

All true (heat, exhaust note and strong smell). It unfortunately still makes for lumpy acceleration and difficulty in stop/start traffic during this regen; it has even caused problems with gearbox shifts, on one occasion going no higher than 4th. All this stops once this regen has cleared, making me think it is a setting or sensor that is at fault. Thank you for your advice.

 

[fox10]

As above and if the car deems the battery is low, it will increase the idle.

Hi hope you can help, I'm a new member and posted my issue up earlier but as yet not been authorised??
Battery warning light comes on showing low voltage (see pic) but while its on my idle is increased to around 1300, switch engine off it idles at normal speed until the red battery light comes on.
Alternator?
Battery?
Voltage regulator?
Many thanks

 

[fox10]

Hi hope you can help, I'm a new member and posted my issue up earlier but as yet not been authorised??
Battery warning light comes on showing low voltage (see pic) but while its on my idle is increased to around 1300, switch engine off it idles at normal speed until the red battery light comes on.
Alternator?
Battery?
Voltage regulator?
Many thanks

 

[brandwooddixon]

Hi welcome to the forum, you'd have done better posting this as a new thread.
Red battery light indicates that he battery isn't charging correctly. (11V is way too low, I would expect 13-14V with the engine running).

The engine management will automatically attempt to compensate for a low battery voltage by increasing the idle speed, as this will increase alternator output, but the question is why is the alternator output so low?
This could be as simple as a loose ancillary belt - tensioners do fail.
Also it could be the regulator on the alternator has failed.

 

[Botus]

All true (heat, exhaust note and strong smell). It unfortunately still makes for lumpy acceleration and difficulty in stop/start traffic during this regen; it has even caused problems with gearbox shifts, on one occasion going no higher than 4th. All this stops once this regen has cleared, making me think it is a setting or sensor that is at fault. Thank you for your advice.

thats the whole point DPF regen should be constant speed 100kph + up to 20km journey down the highway at increased engine revs and engine temperatures till it knows its happy - if you only drive in traffic it will fail - first it will keep attempting to do it - then if you don't do a long, fast enough run for it to believe it has cleaned enough of the soot from the DPF it may get worse....

NOTE: on early cars all the software and sensors on the emiision side are a muddled joke that never really coped with life.... 7th generation DPF sensors came out 5 years ago