The rectangle mounted to the top of firewall

Is this a Camaro or a Firebird? And can you tell us what year this is? It may not make any difference, but is the car an automatic or manual trans? The more information you give, the better it is for us to narrow it down.

It's a 1988 camaro with a 355 carb ,iam re-installing the a.c. system and I am trying to figure out the wiring harness, and there a plug that goes to this and I don't know what it is or doe

that is the MAP sensor-tells the ECM how much vacume the engine is pulling.MAP sensor location varies with different years and engines,'84 up carbed v8s have a same appearance BARO sensor in that location.

I had a hunch that might be what it was. It is not in that location on my Firebird, which is why I was asking what model Thirdgen this was.

just a standard GM MAP sensor...

On yet another one of GM's stamped steel brackets fastened with a regular sheet metal screw. In some ways GM made these engines bays look so cheap and thrown together.

Shouldn't That Be Mounted Underneath The Cowl.

i believe it should be under the cowl

these cars were cheaply built and thrown together..

88 was mass air.

100% agree, but that is definitely a MAP sensor.

Something doesnt match.