Exhaust Fumes

Hi, When I open a window or sunroof in my 94 citroen zx 2.0i petrol, exhaust fumes enter the cabin.

There is no leak in the exhaust. If I keep the windows up, no smell. Turning on blower doesnt cause fumes to enter either.

There seems to be an excess petrol smell from the exhaust when I nose around the rear of the car but nothing under the hood. All dry no obvious leaks.

Other symptoms which might be related are;

-can be hard to start sometimes. Doesnt matter if hot or cold. Turn it over and over and nothing. Turn it off then start again and it fires straight away.
-engine cuts out easily when starting from cold.
-the engine sometimes idles eratically
-sometimes cuts out when approaching a stop. Can start it again immediately
-fuel consumption seems higher than normal (than when I first got the car)

From reading other posts, the injectors or fuel pressure regulator might be an issue. What do you think?

thanks very much.