Hello. Hopefully someone can help, does anyone know what can cause this. Is some vent blocked somewhere? Car is a euro 1989
Yes, it's a valve that is stuck that may cause this, namely part nr 139568 located on the top left side of the engine compartment, take it out, spray some WD40 in it and shake it until you can hear a ball ticking again while shaking.
I had the same issue and at one point is was difficult to loosen the fuel cap due to the pressure behind. Took a look at the "turnover valve" and yes, the valve had failed. Could not blow air through the direction needed. Replaced it and all good now for the last several years. Easy fix.
