not sure what to do or how to get it checked out

i have a 1991 chevy lumina 3.1 6vwhen my car is warmed or up to temp i guess. my idle bogs down and dies every now and then. and recently its been worse. usually when i'm in gear and slowing to a stop or red light. once i pull up my car starts sounding . lkes its strugiling to stay running . most times at stop i have to put it into nutral to stop it from stalling . it still sounds like its droping out , but not as bad and it prevents the stall. my check engin light was on. so i went to autozone and they pulled my code. with was an air sesor. he took me out to my car to show me where it was . and it wasn't even plugged in for some reason. so my check engin light no longer comes on. and my problem is still there. can anyone estimate what it might cost . to just drop it off some where and say find the problem. lol i mean just searching for the problem couldnt add up that much could it ?i dont know it just seems driving anything over 40 mph runs good. below that in residential it sucks. and idle drops while at stops . any help would be great.

Many things can cause this I would start with cleaning the throttle body and remove the idle air control clean the pintle and the passages in the throttle body. Also try disconnecting the egr for test purposes.

Idle air control sounds like the culprit, but like Maxwedge said clean throttle body also. Also check for other vacuum leaks (this should include unplugging EGR valve per Maxwedge).
Price for diagnosis would depend on how long it takes to find the problem, at how much per hour at whatever shop it is taken to.

Start with the basics. Check for vacuum leaks first, and then exhaust leaks. All must be sealed up. Look for cracked or loose vacuum hoses going to the fuel pressure regulator, MAP sensor, vacuum purge valve for the carbon canister, and the carbon canister itself, probably located in the rear of the car near the side quarter panel. Clean the intake throttle body and IAV valve. Check for intake manifold leaks by spraying carb cleaner around the gasket with the car running, if the engine speeds up, there is a leak. Check my other posts for 1990 Lumina.

Good advice but look at the dates, this is 1.5 yeras old and inactive, thanks.

Someone might read this for information about a current problem.