Why are the cars locked while rear door still opened

At speed,( 45-65 mph), my car is belching white smoke and loses power for a few seconds, then quits smoking and power restored. A few miles later, it does the same thing again, and again, and again.

Relay for the secondary air pump
What size is it?

I sometimes feel like my car has a noise like diesel engine,but it's petrol. I mostly hear the noise on the passenger side in the engine. Never attempted to open it up coz i know very little about car… 

Dash and tail lights went out