Stalling and low idle Revs

[Metal Head]

Hi
I recently had a friend look at my polo when he discovered a hole in the vacuum tube, he fixed the tube and then the engine was then reving at about 500 rpm. The engine bounced up between 400 and 600 and stalled. I took the car to the garage and they changed the fuel/air mixture,fitted new spark plugs and changed the thermometer. The car seemed fine, reving at about 900rpm idle, but i went for a drive and at a junction the car rev's dropped again to 500 rpm then started bouncing between 400 and 600 then stalled. This happens pretty much every car journey, the car drives fine and then starts struggling and stalls ten minutes later. Does anyone have any ideas what the problem could be. It seems very un predicatable. One journey the car will be fine, the next it will give me alot of aggro.
Thanks for your help

[Polo Paul]

Mine did this a while back, simple-ish fix if it is what i think it is.

I think its a dirty idle valve, take off the airbox cover and its the hole in the middle with the butterfly if its a 1.4 or 1.0. Get a rag and give it a damn good clean out, use WD40 if you need to but use sparingly.

[Ant_6n]

carb cleaner is better than wd40, if this doesnt work you may need a new temp. sensor i think its a sensor down there anyway.

[loud]

best tool for the job is carb cleaner, a few rags and cotton buds for the hard to reach bits.

if you reach round the back of it you can find the bit to open and close the valve, makes it a lot easier to clean