Just bought a 1999 Ford Galaxy. Revs take time to idle when coming to stop and you can't half hear the engine ticking. Now it has done 148,000 miles. How do I fix this?

possibly an air leak, possibly on inlet manifold...

Idle issue could be, as mentioned, an air leak, gunk in the throttle body meaning it doesnt shut instantly, a sensor down effecting the mixture....

Ticking could also be a number of things, a lifter would be my first suggestion, but it could be one of many things - try and oil change....

Try taking off Idle Control Valve and cleaning it out with carb cleaner, and also what StuyMac said, clean out the throttle body with carb cleaner.