C5 2001 engine sometimes stalls when coasting to a halt

[skycat61]

Hi.

My C5 2.0l 16V 2001 (EW10J4 petrol engine) has developed a curious fault that i have not been able to find mentioned anywhere on the internet so i thought I'd ask the forum for its ideas. When coasting to a halt the engine revs sometimes drops very low and stalls. I've had it on an ODB2 reader and the following codes are present:-

P0352 PRIMARY/SECONDARY IGNITION CIRCUIT COIL B (2)
- FAULTY SIGNAL FUNCTION
- MISSING/HESITATION
This fault has been present for at least 2 years and I do not believe it is related to the current problem.

P0502 VEHICLE SPEED SENSOR
- SIGNAL TOO LOW

P0410 SECONDARY AIR INJECTION SYSTEM MALFUNCTION
This fault is related to an anti pollution system that is only active for the first 90 seconds after starting so I suspect its a red herring.

Apart from the fault the car drives smoothly and returns about 28MPG on the urban cycle.

Any ideas please?

Donald.

[myglaren]

A bit of a shot in the dark but if you read this part of Simon's Blog about carbon on the throttle plate you might be heading in the right direction.

[skycat61]

I checked the throttle plate and there was a carbon build up which I cleaned off with carburetor cleaner and a toothbrush but there has been no improvement. Does anybody know where the vehicle speed sensor is on a C5?

Donald.

[myglaren]

I may get shot down in flames for this but I believe that the speed is taken from the ABS sensors.

[skycat61]

Many thanks. Would that be all 4 sensors or just one?

[VertVega]

One ABS sensor would be enough to raise that error message. That error seems to be a temporary one and most probably your ABS is working fine at the moment. Otherwise a permanent error in the system would be very well seen and heard when you start the engine.

In mine I checked the service history and there was a mention that faulty temperature sensor (of what?) has been replaced. It caused the car to stall. Car works fine during my ownership and never caused such a problem.