1991 Opel Monza Carburetor problem die

We don't have that vehicle here but here are some general recommendations.

First eliminate all vacuum or air leaks in the system. You may have a bad IAC ( idle air control) but try cleaning the throttle body first. Remove the intake snorkel, have someone hold the throttle wide open for you and scrub the back side of the throttle plate and surrounding bore with an old tooth brush and some carb cleaner. Be sure to spray some into the small holes next to the throttle plate. That should help stabilize the idle. If it still has a problem, replace the IAC.

Thanks for the help it work fine after I clean the throttle with carb cleaner.

Those recommendations mainly apply to a fuel injected engine which I suspect this is. We have not had any carbureted engines here in the US since the early 80s.

No I have carburetor engine but they worked just fine. Now I can even start my car from outside and I did a minor service on Saturday(plugs,oil fitter,petrol filter, air filter and grain old oil.