Revs bouncing between 300-1000 @ idle

[Holgate End]

Whenever I slow down and then dip the clutch as I am stopping, or when I actually stop, the revs needle just bounces between about 300 and 1000 revs for a few seconds before settling down to idle at around 7-800.

Also, when slowing down from a slow speed (like when stuck in traffic etc) and the revs are bouncing between 300-1000 as described above, the brake pedal cushions hard and soft - similar to when braking hard where the abs coaxes the car to a stop rather than locking up.

It is very weird, and has started only 2 days after getting it back from having a new alternator fitted (the car was sat in the garage for 6 days without moving - the longest its gone without being started for at least the 2 years I've owned it). 

Anyone got any ideas as to what could be wrong??

[dai-cymru]

could have knocked a wire or connector somewhere when doing the alternator, 

[Fatty B]

could be a few things check the brake servo vacuum hose at the back of the engine if this is cracked can cause hard brake pedal also air leak so idle will move about. Also could be throttle body fault as there would have disconnected the battery to change the alternator may have knocked out the basic setting causing irratic idle chance are its the throttle body.

[Holgate End]

Have just seen Fatty's post, so will have to get it looked at, but this is still happening.

It is only happening at slow speeds and low revs, when I'm in traffic or slowing to a stop for traffic lights etc.  It seems to happen less often (sometimes not at all) if I have the rear windscreen demister turned off and the interior blowers on setting 1 or 2 - which makes me wonder if it is something alternator/battery related. 

Has anyone had this before??  I'd rather have an idea of what it could be before going to a garage and getting bullsh!tted again!!  Cheers.

[golfgtidan]

mine does this, its done it ever since i changed the battery for a lower power one as it was a freebie was a shame not to use it.  wouldnt like to say its the cause of your problem tho...