Engine hesitation problem. Can someone help?

Hi all, I have a 1989 Chevy Conversion van with a 350 throttle body injection system. Recently it has started to hesitate after I have been running it and stop at say a store for 20 minutes. Then when I get back in and start it it runs rough almost like it's loading up. I have to baby the accelerator barely pushing it until it clears up which can take up to 5 minutes. The engine seems to have almost no power during this time. Meanwhile the exhaust has a strange smell. Not like a converter but just semi burned fuel, which kinda burns the eyes. Once it clears up it runs great again. Any thoughts? Thanks. Chris