Bad Idle

[Danr]

Ok my mk1 1800 8v (well 1.9 8v but cant c there being any difference) has decided to go crazy, when the car starts it idles at 1200rpm then after drivuing for a while either fast or normal it drops to about 500 or just drops to 0 when u stop, car will start fine the run do same after a while but sometimes it will idle at 200 and not die, the car does have fast road cams but they have been fine and fault only stared the other night

any ideas on what to do  

[mk1]

Check there are no vacuum leaks, there is a idle adjustment screw on the bulkhead side of the throttle body. When the engine is hot adjust it (out is faster) to give a idle speed of around 950 rpm.
Steve.

[Danr]

BUt would it just go for no reason, as it had been running really well lately  

[mk1]

Check all the pipes and hoses especially the pleated rubber pipe on the metering unit and throttle body. Could have a small air leak witch will allow unmetered air into the engine causing a weak mixture.
Steve.