1998 BMW 528 wagon has throttle dip/surge upon startup, then dies

After you restart it, she runs great. It seems worse when its cold out, but does happen all the time. She starts up just fine but if you let her sit and idle the throttle will dip every 20 seconds or so. Each dip gets lower and lower in the RPM range until it just shuts off. Then if you restart it, it’ll run just fine.

160k if i recall

any thoughts? thanks a bunch, Benji