My brother has an 85 firebird with a 2.8 V6, when we first got the car it wouldn’t idle, when I started working on it I found a missing rubber gasket on the air intake that was making a big vacuum leak, once I replaced it the car ran fine, but when I drove the car around for a while yesterday, I was on the highway the car completely shut off, when I went to start it it started right up and ran fine, once I got it home it stalled again and now it’s running the same as when I first got it, not idling at all, and is throwing a check engine code for the VSS and mass airflow sensor. I checked for vacuum leaks and can’t find any, I was planning on replacing the spark plugs, wires, distributor cap and rotor this weekend, I’m also going to drain out the gas bc I’m not sure how old the gas in it is, and I’ve already replaced the idle air control valve, air filter and put in a good used mass airflow sensor, are there any other parts that would be worth replacing while I’m working on the car? The engine itself seems strong, as soon as it’s idled up it runs smooth, no knocks or skips

 

I was having similar problems a few years ago with my Formula. Thanks to this forum I found out my PCM was bad. I had to get the car to not put out any codes. I pulled the PCM and when its was running normally I knocked on it and boom! Up came the codes, car ran like crap.
I would check the timing as well. My car was advanced way over, ran but would die at idle once in a while. Got that fixed about a month ago. I also put in a new gas pump, Southbay fuel injectors and distributor 2 years ago

 

One more thing you can do. If you know anyone who has a fog or smoke making machine, used for Halloween, etc. You can attach it to a vacuum line and pump it through. Where you see smoke you have a leak. I did this a few years ago and it works great.

 

I found this broken wire behind the engine, it looks like it’s the ground wire to somthing, does anyone know what this goes to?

 

I found the problem, it was a bad Idle Air Control valve, I was able to diagnose it by jumping the top two pins together on the OBD port, if the IACV is working right you should be able to feel it clicking, mine wasn't doing anything, when I replaced it the car was running as good as it had before it broke.