erratic idling and phony battry failure

Hi I have a 1999 1600 OCTAVIA WITH PETROL INJECTION

Just lately three strange things happened

1 QUITE OFTEN THE INSTRUMENTS RPM AND MILOMETER SWITCH OFF TOGETHER ONLY TO REAPPEAR 5 MINUITES LATER

2 The idling is sometimes much slower than before and tonight while i was waiting a long time in a car park the air bag light switched on then the engines revs started swinging low and back again i opened the bonnet and heard a kind of buzzing with the same frquency as the engine revs after a few minuites she stalled and wouldn't start with symptoms like a dead battery.

After waiting and trying a few times she started and went 15Km without a problem and stalled at the drive when I breaked I tried the starter and she whirled back into action can any body help me out there!

best wishes to all fellow skoda owners