99 sierra during cold starts idle surges

I have a 99 Sierra with the 5.3 liter V8. On cold starts it surges really bad from around 1300 rpm to almost stalling. I just noticed that there is a slight smell of gas while it surges. After it warms up it continues to surge lightly until it gets to full operating temperture. When its been driven for a while it's fine on the restart. Just recently the service engine light came on. My first thought was CTS but the symptoms aren't quite right. Any other ideas? Thanks Mike