Why does the TD5 idle change when you roll in Neutral

[BilboBoggles]

My TD5 has done this since new. When you stop and the engine is idling, and if you roll forward slightly under gravity without touching the gears or clutch, then the engine will change the idle slightly and go into a soft rolling rough idle. The rocking idle will persist for a few seconds after you stop and then it idles smoothly. Somewhere there must be a connection between the road speed sensor or perhaps the ABS sensors and the ECU that causes it to change it's idle map.

This also occurs when coasting to a stop at the lights in neutral.

I don't think this is a problem, and I suspect all TD5's do this - I just wonder why?

[PhilipA]

Mine does this on overrun to a stop.
probably to save fuel.
Regards Philip A

[OffTrack]

Only the EU3 maps do this. I've got a EU2 with a modified EU3 map installed and I get the grr grr grr over-run idle. If I switch back to an EU2 map it's gone instantly. First time it happened I thought I'd got a faulty remap

Apparently it's completely normal on the EU3 motors and most noticeable if you have an auto.

[2 rocks]

Only the EU3 maps do this. I've got a EU2 with a modified EU3 map installed and I get the grr grr grr over-run idle. If I switch back to an EU2 map it's gone instantly. First time it happened I thought I'd got a faulty remap

Apparently it's completely normal on the EU3 motors and most noticeable if you have an auto.

Hi OT
Thanks for that - I always notice my D2 auto doing this as I coast up to a stop, as you say is a grr grr grrr - which - being attached to the auto means a slight 'surging' feeling.
Oh well, I thought it was heading for 'box number 3 but happily it seems not!
(I have a re-map but have no idea what the PO put in it).
Cheers
Mike

[justinc]

Paul has hit the nail, the EU3 maps have a cylinder cut on 'overrun' to lessen emmisions, when at low revs and low speeds in a manual version it is disconcerting as it feels like the engine is missing/ about to stall.

JC

[landcol]

Good thread! I've been wondering about this I've an eu3 motor and does this exactly, was stressing it wasn't a dodgy injector. Seems Justin has clarified!