Drivers who refuse to switch off engines while stationary in Westminster are set to be fined £20.
A team of traffic marshals will patrol the borough and ask motorists with idling engines to turn them off when the new policy is implemented from 1 May 2015.
The scheme reflects concerns from residents and businesses about the borough's air quality, Westminster City Council said, and described the penalties as a "last resort."
The Highway Code says parked vehicles must switch off their engines.
The policy follows on from Islington Council's fines for vehicles that idle which was introduced in August and Camden council's for buses that idle for too long, introduced in 2011.
A report by the council in April 2014 said that Westminster has the highest proportion of deaths attributable to air pollution, excluding the City of London, in the country.
"Our residents are rightly concerned about the quality of the air they breathe and the council is committed to improving air quality in Westminster," said Cllr Heather Acton, cabinet member for substantiality and parking.
"Motor traffic plays an important role in keeping our city moving, which is vital for its economic prosperity. We want to raise motorist awareness of the impact engine idling can have on the environment, with air and noise pollution affecting overall health, as well as it being an unnecessary use of fuel," said Acton.