Infuriating engine problem

This started a while ago, and I basically let the car sit because I didn't have the money to fix it. But now I do.

THe problem was when decelerating and depressing the clutch the RPMs would drop, and keep dropping to 0 and the car would stall. At the time the alternator was fine and battery was brand new. A year later when I finally get it back on the road I take it to the shop. The alternator and battery are completely shot at this point and they replace it, saying it should have fixed the problem.

However it didn't. The RPMs will still drop to 0 when decelerating, and stall. It stalled 3 times on my way home, luckily the battery was new, and I could start right back up and drive.

Does anyone ahve any idea what I might be looking at here? Id there a faulty wire somewhere, the shop said it could be a clogged throttle body. Any help is appreciated because I don't want the shop to do a fishing expedition and end up charging me way too much money. Lastly, this is a trusted shop, so they wouldn't be trying to rip me off.

It sounds like your IAC is faulty. When you turn on the AC or turn the wheel, your RPMs should bump up, if they do not, the IAC is bad. Get it fixed because it can over current and destroy the ECU.

Thanks, will check that out now.

edit: Yep, no increase in RPMs when doing those two things. 3SX has a non-oem one for 90, might just look into replacing it with that, unless anyone has recommendations against it?

Rock Auto has them for around $60 last I checked and it is just like OEM.
AC99 is the part number.

Rock Auto FTW for these sensors... don't overpay. The IAC from Rock Auto also is used in the Hyundai and Kia 6G72 engines.

I had that same problem when I had a boost leak running open BOV on a stock MAFS. Tightened everything up and it worked fine. Definitely check the IAC though, those are notorious for going out