After a year or so of my ZX (1995 1.9D, 139,500) getting more and more asthmatic, to the point where it was getting embarrassing on steep hills, I finally had the injectors serviced. Woo-hoo...! What a difference. It now starts easier, it doesn't puff out clouds of blue smoke when starting, it's got rid of the annoying chugging at idle which made me think there was a misfire, and it goes like whatsit off a shovel. OK, not cheap (£192), but worth it in sheer drivability.
There's only one downside; the extra power has brought to light a slipping clutch which won't adjust out, so guess what my next job is...
Phil