86 Iroc Engine Problems

My brother in law has a 86 Iroc and his problem is that the engine dies when cold but will run when it's warmed up. He's changed just about all of the sensors. plugs, wires and even checked the IAC motor but still can't find the problem. Whats really strange is it will actually run fine if the air filter is off but as soon as he puts it back on it will die. I know it's an 8 cyl. but don't know what size. I've been trying to help him out, but we are both out of ideas. Is there anybody out there that can offer any help on this matter? Thank you for any information you can offer.

Try your cold start valve. It is a ninth injector in the middle of the runner tubes on the driver side. Atleast I think that is what it is...LOL

Clearly_Canadian

You may want to check the coolant temperature sensor. If it isn't working properly, it makes the ECU think that the engine is already warm so it doesn't adjust the fuel mixture, however it'll run fine once warmed up.