Had similar probs myself...and now feeling hugely chuffed that it's running better than ever!

How? Quite easy and very cheaply. 1 can of electrical contact cleaner, 1 can of carb cleaner, 1 tub of vaseline and half a dozen hours.

Disconnect battery, then disconnect every electrical connection (1 at a time) ie supplementary air valve , cold startvalve, engine sensors...every connector you can see. Spray terminals and plugs with the contact cleaner and "work" the connection (some of mine had a lot of corrosion on them) Smear some vaseline on the connector...this will keep them corrosion free.
Also cleaned up terminals on battery, body earths, starter connections.

Next remove the throttle body and unscew (count the number of turns to remove) the idle speed screw. Spray carb cleaner up the idle speed screw passage - mine was full of gunge. Clean the throttle butterfly and body. Re-instal the throttle body and idle speed screw...screw in the same number of turns as it took to remove, to give rough idle speed setting.

Supplementary air valve (bolted under inlet manifold) Remove and clean out with carb cleaner followed by WD40 - re-instal.

Connect battery and start, warm up and set idle speed....absolutely wonderful. Smooth and steady idle speed, clean pick up and catches straight away from cold :top

All very simple and basic. Also make sure all breather pipes are clear and not cracked...and make sure the oil dipstick is firmly located in the tube!

Hope this is of help

Rhys