I hope you use spray with the straw like thing provided with it. If the car runs fine after service for few weeks, then to me (being a beginner), it looks like you need to focus more on 'filtration' process of fuel.
Like margallar mentioned, I saw double fuel filters in some cars, which was installed right after fuel pump outlet pipe.
Spray carburetor cleaner every week or every two weeks, even if the car works fine.
Avoid keeping fuel level lower than quarter, as all the residue settles down at the bottom of fuel tank.
Change petrol station too. F-6 Super Market Caltex pump has clean and better quality petrol.
For now, check all vacuum pipes first, especially the ones on red thing (intake manifold). They maybe leaking, causing idling problems.