Hi All Please help

I have a 190e w201 2.0 on a 92 plate. The problem I have is getting worse

The car starts first time everytime and idles at 1000rpm at first after about 3 minutes the car then struggles and cuts out running about 450-500 rpm. after the cars engine is at 80oc running tempriture it runs fine at 800rpm idle.

I have changed the cold start valve, sparks plugs, ht leads, distrubitor, and the car gets a regular service.

any ideas would be appreciated

Thanks Ian