I have an 88 VW Cabby, and sometimes it runs fine, and is great (will pass smog) but recently it has been idling and running rough, I think it's rich, because the engine fluctuates, kind of like you hear those supercharged drag racers doing, and it's an intermittent problem.

The engine starts up and idles fine sometimes, then I will hear a click and the problem will start, could it be one of my sensors? Like the O2 sensor? and the radiator fan doesn't always come on, and it causes my car to minorly overheat sometimes. Any help would be appreciated.