It counteracts the effect of leaking main injectors, or rich idle mixture, or a faulty sensor............. but only up to a point. If it starts after disconnection then it points to being to rich, you then have the task of finding out why!
With 20 year old fuel metering units it could even be the fuel pressure creeping up as they no longer stay calibrated/set like they did from new, this is one of the problems with MFI RST's.