1989 Chevy Camaro Camaro

When does this happen when coming to a stop or will it happen driving on the highway too

I think a good throttle body cleaning and throttle plate cleaning, then check/clean or replace the idle air control valve will clear you right up

This is an 89 so it should have one, it will be located right on the throttlebody, right before the throttle plate, typically. It should have two wires going to it, also on the throttle body is the tps, so dont get them confused, did you say you've changed the gas filter? I would still do that, and yes your injector is mostlikely clogged, and will need replacement, this is where the conveinance and affordability of junk yards and salvage yards come in, I would go to one of those yards where I can pull everything off myself, most times they will give you things like an injector for free. Alot of people just pop em in their pockets, not implying that is what you should do, but it happens.