Engine revs slow to return to idle

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My Name: Paul

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Posts: 17
Joined: Wed Oct 10, 2018 8:49 am
Model: C3 Picasso
Year: 2010 (10)
Engine Size: 1.6
Fuel Type: Diesel
Mileage: 75029
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: Yes
LHD or RHD: RHD (UK)
Engine name: DV4 diesel (70 PS)
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I have replaced my C3 with a slightly older Picasso because I needed more space. This car has done 53000 miles and has a full service history. It has the Puretech 110 engine.

The problem is that when you take your foot off the throttle there is a delay in returning to idle. It hangs at about 1500 rpm for a second or so. I've searched and cannot find a ref to this problem specifically for this engine and don't seem to be able to find things like replacement MAF sensors etc listed. The car has a short warranty and I guess I will take it back to the dealer but I would like to have some background as to what the problem is likely to be so I can speak on level terms with him.

Any info would be appreciated, thanks
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My Name: Ozvtr

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Posts: 936
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
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I am not that familiar with the Puretech engines however has it done this all the time or only just started doing this?
Does the engine light come on?
The throttle body butterfly can get gunge around the inlet and cause it to stick, but this should cause a "coherence" fault between the peddle and the throttle.
My Name: Paul

Contributor
Posts: 17
Joined: Wed Oct 10, 2018 8:49 am
Model: C3 Picasso
Year: 2010 (10)
Engine Size: 1.6
Fuel Type: Diesel
Mileage: 75029
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: Yes
LHD or RHD: RHD (UK)
Engine name: DV4 diesel (70 PS)
Has thanked: 1 time
Been thanked: 6 times

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I've only had the vehicle a couple of weeks.

The pedal returns ok and the problem only happens when you go over a certain revs, I'm guessing maybe about 2000rpm such as a quick start from standstill. However it happens up through the gears as well when you take your foot off the pedal to change up. It also happens when you decelerate such as in traffic and I sometimes have to dip the clutch or it is still trying to drive.

It only hangs at about 1500rpm and only for a second or two. It's enough though to make you adjust your driving to it.
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My Name: Ozvtr

Moderator
Posts: 936
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 36 times
Been thanked: 250 times

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Paul wrote: Sat May 15, 2021 1:57 pm I've only had the vehicle a couple of weeks.

The pedal returns ok and the problem only happens when you go over a certain revs, I'm guessing maybe about 2000rpm such as a quick start from standstill. However it happens up through the gears as well when you take your foot off the pedal to change up. It also happens when you decelerate such as in traffic and I sometimes have to dip the clutch or it is still trying to drive.

It only hangs at about 1500rpm and only for a second or two. It's enough though to make you adjust your driving to it.
The pedals are very reliable and rarely have problems.
The throttle body sticking is the only thing I can think of.
I can only suggest removing the air cleaner housing from the throttle body and have a look at it. It will either be clean or have black crap around the point where the butterfly valve meets the walls of the throttle body.
My Name: Paul

Contributor
Posts: 17
Joined: Wed Oct 10, 2018 8:49 am
Model: C3 Picasso
Year: 2010 (10)
Engine Size: 1.6
Fuel Type: Diesel
Mileage: 75029
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: Yes
LHD or RHD: RHD (UK)
Engine name: DV4 diesel (70 PS)
Has thanked: 1 time
Been thanked: 6 times

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OK thanks I'll check that out.

A couple of points.....I don't think it's an air leak as the idle is stable, no hunting or surging etc. Plus it only happens at a given point in the rev range.

I've done quite extensive searches on the net and found similar problems with other cars but no reference to Citroen. It appears to be a characteristic of some Ford cars and lots of mentions in relation to Ford |Mustangs. In that case it seems the car is actually programmed to hang the revs on deceleration so as to reduce emissions. It seems that when you close off the throttle emissions soar, however if this was the case with the Puretech engine one would think there would be some mention of it somewhere.

I wonder if anyone else has had the problem. I can't believe mine is the only one or do others assume it is a characteristic of the car?
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My Name: Ozvtr

Moderator
Posts: 936
Joined: Wed Jul 10, 2019 3:31 am
Model: C3 2002-2005, Original shape model
Year: 2003 (53)
Engine Size: 1.4 (8v)
Fuel Type: Petrol
Mileage: 80000
Trim Level: Other
Gearbox: Automatic PRND
DPF: No
LHD or RHD: RHD
Engine name: TU3 (75 PS)
Location: Brisbane, Australia.
Has thanked: 36 times
Been thanked: 250 times

Post

Paul wrote: Sun May 16, 2021 10:22 pm In that case it seems the car is actually programmed to hang the revs on deceleration so as to reduce emissions. It seems that when you close off the throttle emissions soar,
In the old days, carburetors had what was known as a dash pot, linked to the butterfly valve. It did the same thing, decelerated the closing of the butterfly. It was mostly to stop back firing because of a sudden rich mixture from the butterfly snapping shut. I guess it helped emissions too. My 1981 Mazda 323 had an 'idle up' vacuum actuator that was electronically driven from the coil points to stop the throttle closing all the way for about a second after the throttle was cut.
I cant see how this can affect a modern car when the engine ECU can cut the fuel when it detects the butterfly closing quickly. However the 'snappy' action of the butterfly valve might cause the response of the engine to be 'jerky'.
Either way the engine should not "hang" between gear changes or cause the car to run on. Even with the dash pots in carbureted cars, they never did that.
My Name: Paul

Contributor
Posts: 17
Joined: Wed Oct 10, 2018 8:49 am
Model: C3 Picasso
Year: 2010 (10)
Engine Size: 1.6
Fuel Type: Diesel
Mileage: 75029
Trim Level: Exclusive
Gearbox: Manual 5 speed
DPF: Yes
LHD or RHD: RHD (UK)
Engine name: DV4 diesel (70 PS)
Has thanked: 1 time
Been thanked: 6 times

Post

Thanks, I'll come back if I get any more information or a solution.
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