Ben answered the same question on another forum... [img]smilies/wink.gif[/img] which I stumbled across [img]smilies/eek.gif[/img]
Read on [img]smilies/cwm29.gif[/img]
Sounds like there is a vacuum leak in your intake system.
The brake servo takes vacuum from the inlet manifold to increase braking efficiency. The idle system should compensate for this but in your case it sounds like its over, then under compensating.
A simple check of the pipes and connections should reveal something, and is best done while the motor is running and someone is pumping the brake pedal.
Dont know what year your car is but I suspect it is a T-Spark motor which has a reasonably complex idle circuit so if the problem is here it's best left to a mechanic to sort.
2x 145, 4x 75, 4x Sprints,a 156, 146 now a 155