idle trouble rough

hi everybody,, i have an early 944 1983 and i,ve got a problem with my engine. When i start my car for the first time of the day everything is ok, but sometime whne i,m starting the car second time,, my RPM drops down very fast, like 1000 rpm to 100 and goes up just to 300 rpm and drop to 100 etc...but if i run the car on the highway the car run well. :screwy: The fuel filter is new, the spark plug too, the old dme have a trouble and run the car too rich and a change it and he was nice until the last week.. if you have any ideas i will appreciate your help

have a nice day

Did the engine do the same with the old DME?

no he doesn't , whit the old DME he was just running very rich and when i was pressing on the accelarator he doesn't take his gas correctly,, and it was a black smoke comme thrue the exaust and somme little backfire appened

Are you sure you got the same series DME?

in Late 85, Porsche changed to a newer DME and it made the two incompatible.

yes i,m very sure about the same DME, i took him from a 1984 and the number on the DME was the same.