ough start-up idle

[jackrussell]

My '83 944 just developed a start-up idle problem. It starts easy on first crank but idles rough at about 400/500, almost dies, but will keep running with foot on accelerator. In about two to three minutes as the engine begins to warm up the idle smooths out to about 900/1000. It runs good on up to full power.
What's wrong? All suggestions will be appreciated. [I'm still old and slow].